textural and stable isotopic evidence for the genesis of the tynagh base metal deposit ireland at the tynagh mine county galway four major stages of mineralization can be recognized that span the diagenetic and postlithification history of the host waulsortian limestones 1 growth of colloform and granular pyrite clots during the early diagenesis of the micritic host 2 rapid geopetal precipitation of microcrystalline sphalerite galena barite and dolomite within a dilatant fracture system that developed as a consequence of the forceful injection of metalliferous fluids into the coherent waulsortian carbonate mudbanks adjacent to the tynagh fault 3 veining and replacement of the host and previously precipitated phases by tennantite chalcopyrite bornite arsenopyrite medium to coarsely crystalline galena and coarse sparry barite and 4 finally precipitation of calcite within veinlets and cavities and dolomitization of large bodies of previously unmineralized waulsortian limestones sulfur isotope ratios indicate that contemporaneous lower carboniferous seawater acted as the source of sulfate for precipitation of barite delta 34 s 21 1 to 17 4ppm stage 1 delta 34 s 3 1 to 15 5ppm and stage 2 delta 34 s 4 1 to 26 0ppm sulfides were precipitated by reduced sulfur generated during open system bacterial reduction of this sea water sulfate source isotopically heavier delta 34 s or 0ppm reduced sulfur of deep seated origin was introduced from the fault zone during stage 3 this mixed with bacteriogenic sulfur migrating into the waulsortian bank limestones to precipitate stage 3 sulfides and sulfosalts delta 34 s 11 1 to 23 0ppm mineralized limestones delta 13 c 2 1 to 4 0ppm delta 18 o 17 6 to 27 1ppm ore stage carbonates delta 13 c 2 8 to 3 4ppm delta 18 o 17 1 to 26 9ppm and postore carbonates delta 13 c 4 0 to 2 6ppm delta 18 o 15 9 to 25 8ppm are depleted in the heavier isotopes of carbon and oxygen with respect to unmineralized limestones delta 13 c 3 1 to 4 1ppm delta 18 o 22 2 to 28 1ppm the depletion in 13 c is attributed to the mixing of host derived carbon with bacterially oxidized carbon and during stage 4 deep seated carbon the 18 o depletion of the mineralized host is a consequence of isotopic exchange with the ore fluids an oxygen isotope fractionation temperature of 200 degrees c and a delta 18 o smow value of 10 5 per mil for the coexisting water is obtained from a single stage 3 quartz albite pair collected from the fault zone if these values are accepted the delta 18 o values of stage 3 carbonates can only be interpreted in terms of mixing of this isotopically heavy water introduced from the fault with isotopically lighter water already present or migrating into the bank limestones

on diagenesis dolomitisation and mineralisation in the irish zn pb orefield marine calcite cementation and lithification of carboniferous carbonate sediments hosting zn pb mineralisation in the irish orefield occurred at or near the seafloor a relatively early fine grained grey replacive dolomite preferentially developed in micrite is widely developed in the waulsortian limestone formation the main host to mineralisation and is pervasive in the southeastern midlands in proximity to the leinster massif this dolomite formed after the first four main stages of calcite cementation but probably also developed within tens of metres of the seafloor as evidenced by incorporation of clasts of dolomite in intraformational sedimentary breccias later coarse grained white dolomite preferentially replaced coarser components of the waulsortian limestone and infilled residual vuggy porosity whilst some of this coarse dolomite may be related to the fine replacive dolomite event a common spatial association with fault zones coupled with primary fluid inclusion data suggest that a significant proportion of this phase precipitated during the onset of fault controlled subsidence and widespread hydrothermal circulation within the irish midlands area fluids up to 250 c and 10 15 wt nacl equivalent sourced from a lower palaeozoic basement equilibrated fluid reservoir infiltrated the carbonate sequence via faults and fractures the more localised development of dolomite cemented breccias white matrix breccias that are frequently associated spatially with mineralisation was a consequence of the increased focusing of these hydrothermal fluids ore formation was broadly synchronous with development of the white dolomite breccias but only happened where mixing occurred between the hydrothermal ore fluids and localised near surface reservoirs of low temperature h2s rich brine in the waulsortian this process led to the precipitation of a distinctive black dolomite that forms a broad halo to massive sulphides although ore stage sulphides postdate significant diagenesis of the host rocks and often display epigenetic textures the fact that much of the cementation occurred soon after carbonate deposition means that mineralisation does not have to have formed after significant burial in fact the occurrence of clasts of hydrothermal dolomite and sulphides in intraformational debris flow breccias is only consistent with mineralising processes occurring in the near seafloor environment relatively soon after host rock deposition the regional development of a distinctive pink dolomite associated with faults and fractures was a post ore event and is considered to mark a regional brine migration linked to the onset of the variscan orogeny the development of this new tectonic and flow regime may have been responsible for the cessation of economic mineralisation in ireland

a review of catastrophic drainage of moraine dammed lakes in british columbia abstract moraine dammed lakes are common in the high mountains of british columbia most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the little ice age many moraine dams in british columbia are susceptible to failure because they are steep sided have relatively low width to height ratios comprise loose poorly sorted sediment and may contain ice cores or interstitial ice in addition the lakes commonly are bordered by steep slopes that are prone to snow and ice avalanches and rockfalls moraine dams generally fail by overtopping and incision the triggering event may be a heavy rainstorm or an avalanche or rockfall that generates waves that overtop the dam the dam can also be overtopped by an influx of water caused by sudden drainage of an upstream ice dammed lake jokulhlaup melting of moraine ice cores and piping are other possible failure mechanisms failures of moraine dams in british columbia produce destructive floods orders of magnitude larger than normal streamflows most outburst floods are characterized by an exponential increase in discharge followed by an abrupt drop to background levels when the water supply is exhausted peak discharges are controlled by dam characteristics the volume of water in the reservoir failure mechanisms and downstream topography and sediment availability for the same potential energy at the dam site floods from moraine dammed lakes have higher peak discharges than floods from glacier dammed lakes the floodwaters may mobilize large amounts of sediment as they travel down steep valleys producing highly mobile debris flows such flows have larger discharges and greater destructive impact than the floods from which they form moraine dam failures in british columbia and elsewhere are most frequent following extended periods of cool climate when large lateral and end moraines are built a period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure this sequence of events occurred only a few times during the holocene epoch most notably during the last several centuries glaciers built large moraines during the little ice age mainly during the 1700s and 1800s and lakes formed behind these moraines when climate warmed in the 1900s twentieth century climate warming is also responsible for recent moraine dam failures in mountains throughout the world warming from the late 1800s until about 1940 and again from 1965 to today destabilized moraine dams with interstitial or core ice the warming also forced glaciers to retreat prompting ice avalanches landslides and jokulhlaups that have destroyed some moraine dams

transient development in confluent and diffluent flow abstract explaining the growth of disturbances superimposed on mean flows is a central problem in meteorology most widely studied models of the development process involve perturbations to shear flows with shear restricted to the meridional direction recently the importance of zonal variation of the mean flow was recognized and the study of shear flows extended to include zonal variation in shear these studies found that the eigenfunctions associated with unstable modes in the simple shear problem are highly sensitive to zonal variation of the mean flow however there also exists another mechanism for development in a zonally inhomogeneous flow field transient growth not associated with exponential instability properly configured perturbations exhibit transient growth in deformation fields associated with regions of confluence and diffluence at rates comparable to development in shear flow in this work analytic solution of the linear initial value problem for the barotropic vorticity equation in de

the geometry and petrogenesis of hydrothermal dolomites at navan ireland the dolomites at navan ireland formed in courceyan peritidal and shallow shelf limestones the dolomite body has a plume like geometry cross cutting both lithological boundaries and diagenetic barriers generated by sea floor cementation and emergence the dolomitizing fluids rose parallel to major faults to diffuse laterally through the succession controlled by variations in permeability that reflect both facies variation on deposition and pre dolomitization diagenesis cathodoluminescent zones reveal three principal stages of dolomite emplacement separated by dissolution surfaces with each stage reflecting several changes in the character of dolomitizing solutions the predominance of dull zones indicates burial rather than surface conditions the dolomites formed some time after burial in response to an areally limited hydrothermally driven flow isotope values 18o of 6 6 to 10 4 and 13c of 0 2 to 2 5 pdb and fluid inclusion data suggest that these fluids had compositions similar to those of carboniferous seawater however these became hotter with time with temperature increasing from 60 to 160 c the navan dolomites are closely associated with europe s largest zinc lead deposit the distribution of the ores follows the same trend as that of the dolomites and paragenetic relationships indicate that dolomitization and mineralization were temporally and genetically related

timing of interplay between hydrothermal and surface fluids in the navan zn pb orebody ireland evidence from metal distribution trends mineral textures and δ34s analyses models of genesis for the navan orebody are of two distinct types an early hypothesis that mesothermal though nonmagmatic deposition of ore began when a supernatant seawater brine still had access to the host sediments during the early to mid mississippian has been challenged by recent suggestions favoring a later mid to late mississippian to pennsylvanian mineralization derived from cooler fluids traversing either the mississippian pennsylvanian basin or the underlying basement from the south these models characterized here as irish type and mississippi valley type respectively are interrogated as to their particular predictions with regard to metal distributions and sulfur isotope patterns associated with various fault geometries the basal 5 lens of the navan zn pb deposit contains 70 percent of the known tonnage of the 90 mt orebody and thus is the focus of this examination lead distribution patterns suggest that migration of metal bearing fluids was principally directed up early to mid mississippian near vertical north northeast northeast and east northeast minor normal faults these faults predate or are coeval with the major extensional partly listric east northeast faults which now control the general disposition of the deposit only where these major east northeast faults cross putative deep seated northeast caledonoid and northwest structures are they associated with lead enrichments a systematic 34 s survey in the 5 lens across five minor north northeast through to east northeast trending faults associated with distinct lead enrichments and one east northeast trending partly listric major extensional fault adjacent to that trend revealed positive 34 s values 1 18 for galena sphalerite and marcasite sampled within 3 m of all the faults on the profile sulfides with positive 34 s values associated with the deep seated metal bearing fluid generating the navan deposit have been highlighted by previous workers anderson et al 1998 the evidence reported here strongly suggests that the metal bearing fluids rose through all the fractures conversely negative 34 s values 1 to 26 were returned in galena and sphalerite sampled 3 m or more from these faults these negative values indicate that locally derived bacteriogenic sulfide reduced from seawater sulfate dominated away from these faults pyrite 34 s values suggest a background level of 29 3 0 per mil across the profile however pyrite 34 s values as low as 34 2 7 per mil were recorded in one sample collected from within 1 m of a fault thus fluids containing highly fractionated bacteriogenic sulfide also gravitated into these faults on at least one occasion there is also evidence suggesting that the metal bearing solutions periodically displaced the locally derived bacteriogenic sulfide bearing fluid in and near the faults mineral sulfide petrography is used to contextualize the sampling and to give a qualitative indication of the degree of chemical disequilibrium of the system mineral textures demonstrating comminution and dissolution are revealed by this study that when coupled with evidence of isotopic overprinting force the conclusion that mineralizing fluids first invaded the host lithologies during mid lower mississippian times coincident with active faulting there is no evidence of reactivation of the minor fault sets encountered in the study area during post chadian tectonism though the major partly listric east northeast extensional faults were reactivated at that time ore deposition was effected by bacteriogenic sulfide reduced from mississippian seawater sulfate reacting with rising metal bearing mesothermal fluids thus any model invoking an onset of mineralization later than the mid lower mississippian does not stand up to this scrutiny

el nino variability off peru during the last 20 000 years here we present a high resolution marine sediment record from the el nino region off the coast of peru spanning the last 20 000 years sea surface temperature photosynthetic pigments and a lithic proxy for el nino flood events on the continent are used as paleo el nino southern oscillation proxy data the onset of stronger el nino activity in peru started around 17 000 calibrated years before the present which is later than modeling experiments show but contemporaneous with the heinrich event 1 maximum el nino activity occurred during the early and late holocene especially during the second and third millennium b p the recurrence period of very strong el nino events is 60 80 years el nino events were weak before and during the beginning of the younger dryas during the middle of the holocene and during medieval times the strength of el nino flood events during the last millennium has positive and negative relationships to global and northern hemisphere temperature reconstructions

circulation structures leading to propagating and non propagating heavy summer rainfall in central north china using 30 years of hourly rain gauge records and reanalysis data this paper reveals two types of heavy summer rainfall in central north china cnc the lasting mountain lm rainfall and the mountain plain mp rainfall and further explains their formation mechanisms the evolutions of the rainfall are found to be closely connected to upper tropospheric temperature anomalies when upper tropospheric warm cold anomalies dominate north china the japan sea and stretch down to lower layers positive negative geopotential anomalies which appear above the warm cold anomalies governed by hydrostatic equilibrium extend from upper to lower troposphere in the lower layers evident low level easterly anomalies form to the south north of the positive negative geopotential center controlling the downstream of cnc and making convective systems difficult to progress eastward correspondingly the low level convergence and strong convection maintain in the west and the rainfall persists over the mountains constituting the lm process but when upper tropospheric cold warm anomalies dominate the west east of 110 e and stretch down to lower layers cnc is situated between an upstream trough and a downstream ridge as the trough ridge system progresses eastward the low level moisture tongue and strong convections in front of the trough move from the mountains to the plains and the rainfall propagates downstream constituting the mp process results in this paper indicate that upper tropospheric temperature has significant influence on the evolution of rainfall and pay attention to its characteristics could provide helpful information in the analysis and forecasting of rainfall propagation

a characteristic life cycle of upper tropospheric cyclogenetic precursors during the experiment on rapidly intensifying cyclones over the atlantic erica abstract this paper documents a characteristic life cycle of upper tropospheric precursors to surface cyclogenesis observed during the field phase of the experiment on rapidly intensifying cyclones over the atlantic erica december 1988 february 1989 this life cycle begins with the development of an elongated region of lower dynamic tropopause that forms in association with an intensifying midtropospheric jet front over central north america the elongated disturbance subsequently compacts into a more circular configuration prior to crossing the east coast of north america and frequently is associated with rapid surface cyclogenesis offshore a representative example of the life cycle outlined above is documented through a detailed case study of the upper precursor associated with the second erica intensive observation period iop 2 cyclone emphasis is placed upon i description of the tropopause structure and evolution during the upper precursor life cycle ii diagnosis of mechanisms leading to t

northern hemisphere 500 hpa trough merger and fracture a climatology and case study abstract the results of an objective climatology of 500hpa trough merger defined as the amalgamation of two initially separate vorticity maxima and trough fracture defined as the splitting of a single vorticity center into two separate vorticity centers are presented for the northern hemisphere the data source is the gridded national meteorological center nmc now the national centers for environmental prediction analyses available on cd rom on the nmc operational octagonal grid 381 km resolution at 60 n for the period september 1957 to may 1989 a total of 2152 3053 merger fracture events are identified merger and fracture events tend to occur preferentially in the band of middle latitude westerlies merger events exhibit a tendency to avoid major mountainous regions and show a somewhat higher frequency of occurrence downstream of these regions fracture events cluster somewhat over eastern ocean basins the southwestern united states and northwestern africa while also avoiding major mount

zn fe and s isotope fractionation in a large hydrothermal system abstract the genesis of hydrothermal ore deposits is of crucial economic importance this study investigates the extent causes and consequences of zinc and iron isotope fractionation in a large hydrothermal system at the world class navan zn pb orebody ireland large variations in zn fe and s isotope compositions have been measured in microdrilled sphalerite zns at the millimetre scale 66 zn and 56 fe display a well defined positive correlation and both also correlate with 34 s these relationships represent the combined effects of kinetic zn and fe isotope fractionation during sphalerite precipitation and s isotope variation through mixing of hot metal rich hydrothermal fluids and cool bacteriogenic sulfide bearing brines combined with s isotope data 56 fe and 66 zn data on mine concentrates confirm that hydrothermal sulfide is a minor component of the overall deposit signature our data suggest that incoming pulses of metal rich hydrothermal fluid triggered sulfide mineralisation and that rapid precipitation of sphalerite from hydrothermal fluids will lead to strong kinetic fractionation of zn and fe isotopes at very short time and length scales thereby limiting the use of fe and zn isotopes as exploration tools within deposits but revealing the possibility of detecting new deposits from isotopically heavy zn fe geochemical halos

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir

hydrothermal alteration of graywacke by brine and seawater roles of alteration and chloride complexing on metal solubilization at 200 degrees and 350 degrees c graywacke was reacted with seawater and with a saturated nacl brine containing ca mg and k using a solid liquid ratio of 1 10 the degree of reaction was minimal at 200 degrees c but significant at 350 degrees c in both fluids anorthite dolomite and some illite and quartz amounting to about 25 percent of the graywacke were converted to smectite chlorite and albite both fluids lost all their mg and gained k ca and co 2 only the brine gained and maintained significant concentrations of heavy metals indicating the importance of chloride complexing chloride concentration in seawater is apparently insufficient for extensive complexing under the experimental conditions chloride complexing however serves only to maintain metals in solution and prevents their reprecipitation as alteration products alteration involving production and consumption of hydrogen ions is required for the release of metals from the source matrix in the experiments mg metasomatism and dedolomitization provided the h super for the process metal solubilization by the brine followed the order of abundance in the graywacke zn ni cu pb sb cd suggesting a common matrix and no selective leaching effect in other words as a given increment of rock was altered all of its component metals were released metal concentration in solution therefore was not limited by sulfide solubility and represents minimum values changes in the bulk composition of the graywacke were minimal except for increases in mg content and the final rock would probably not be recognized as an altered source rock in the field the fluids generated during the experiments would likely subject wall rock at the site of ore deposition to hydrolytic alteration including potassium metasomatism

baroclinic development within zonally varying flows previous idealized modelling studies have shown the importance of across jet barotropic shear to the resulting evolution of cyclones anticyclones surface based fronts and upper level fronts meanwhile many observational studies of cyclones have shown the importance of along jet variations in the horizontal wind speed i e confluence and diffluence this study investigates the importance of these along jet zonal for zonally oriented jets variations in the horizontal wind speed to the resulting structures and evolutions of baroclinic waves using idealized models of growing baroclinic waves an idealized primitive equation channel model is configured with growing baroclinic perturbations embedded within confluent and diffluent background flows when the baroclinic perturbations are placed in background confluence the lower tropospheric frontal structure and evolution initially resemble the shapiro keyser cyclone model with a zonally oriented cyclone strong warm front and bent back warm front later as the baroclinic wave is amplified in the stronger downstream baroclinicity the warm sector of the cyclone narrows becoming more reminiscent of the norwegian cyclone model the upper level frontal structure develops with a southwest northeast orientation and becomes strongest at the base of the trough where geostrophic cold advection is occurring in contrast when the baroclinic perturbations are placed in background diffluence the lower tropospheric frontal structure and evolution resemble the norwegian cyclone model with a meridionally oriented cyclone strong cold front and occluded front the upper level frontal structure is initially oriented northwest southeast on the western side of the trough before becoming zonally oriented weak geostrophic temperature advection occurs along its length these results are compared to those from previous observational and idealized modelling studies copyright 2007 royal meteorological society

giant landslides in the foreland of the patagonian ice sheet abstract quaternary glaciations have repeatedly shaped large tracts of the andean foreland its spectacular large glacial lakes staircases of moraine ridges and extensive outwash plains have inspired generations of scientists to reconstruct the processes magnitude and timing of ice build up and decay at the mountain front surprisingly few of these studies noticed many dozens of giant 108 m3 mass wasting deposits in the foreland we report some of the world s largest terrestrial landslides in the eastern piedmont of the patagonian ice sheet pis along the traces of the former lago buenos aires and lago puyerredon glacier lobes and lakes more than 283 large rotational slides and lateral spreads followed by debris slides earthflows rotational and translational rockslides complex slides and few large rock avalanches detached some 164 56 km3 of material from the slopes of volcanic mesetas lake bounding moraines and river gorge walls many of these landslide deposits intersect with well dated moraine ridges or former glacial lake shorelines and offer opportunities for relative dating of slope failure we estimate that 60 of the landslide volume 96 km3 detached after the last glacial maximum lgm giant slope failures cross cutting shorelines of a large late glacial to early holocene lake glacial lake pis likely occurred during successive lake level drop between 11 5 and 8 ka and some of them are the largest hitherto documented landslides in moraines we conclude that 1 large portions of terminal moraines can fail catastrophically several thousand years after emplacement 2 slopes formed by weak bedrock or unconsolidated glacial deposits bordering glacial lakes can release extremely large landslides and 3 landslides still occur in the piedmont particularly along postglacial gorges cut in response to falling lake levels

modeling glacier thickness distribution and bed topography over entire mountain ranges with glabtop application of a fast and robust approach 1 the combination of glacier outlines with digital elevation models dems opens new dimensions for research on climate change impacts over entire mountain chains of particular interest is the modeling of glacier thickness distribution where several new approaches were proposed recently the tool applied herein glabtop glacier bed topography is a fast and robust approach to model thickness distribution and bed topography for large glacier samples using a geographic information system gis the method is based on an empirical relation between average basal shear stress and elevation range of individual glaciers calibrated with geometric information from paleoglaciers and validated with radio echo soundings on contemporary glaciers it represents an alternative and independent test possibility for approaches based on mass conservation and flow as an example for using glabtop in entire mountain ranges we here present the modeled ice thickness distribution and bed topography for all swiss glaciers along with a geomorphometric analysis of glacier characteristics and the overdeepenings found in the modeled glacier bed these overdeepenings can be seen as potential sites for future lake formation and are thus highly relevant in connection with hydropower production and natural hazards the thickest ice of the largest glaciers rests on weakly inclined bedrock at comparably low elevations resulting in a limited potential for a terminus retreat to higher elevations the calculated total glacier volume for all swiss glaciers is 75 22 km3 for 1973 and 65 20 km3 in 1999 considering an uncertainty range of 30 these results are in good agreement with estimates from other approaches

ice core palaeoclimate records in tropical south america since the last glacial maximum ice core records spanning the last 25 000 yr from the tropical andes of south america are reviewed these records from quelccaya huascaran and sajama present a high temporal resolution picture of both the late glacial stage lgs and the holocene climatic and environmental conditions in the south american andes late glacial stage conditions at high elevations appear to have been cooler than today although the magnitude of the inferred cooling differs with the particular proxy used e g snowline depression pollen ice cores insoluble dust and anion concentrations in the ice cores reveal that lgs hydrological conditions in the tropics 9 s were much drier than today whereas in the subtropics 18 s lgs conditions were much wetter this probably reflects the migration of the tropical hadley cell in response to a different meridional temperature gradient low nitrate concentrations in the lgs ice from both huascaran and sajama suggest that the amazon basin forest cover may have been much less extensive discussed is the conundrum surrounding the use of d 18 o as a palaeothermometer in the tropics where temperatures exhibit little seasonal variation yet the ice core records suggest that d 18 o records temperature variations on decadal to millennial time scales finally evidence is presented for a strong twentieth century warming copyright 2000 john wiley sons ltd

genesis of the silvermines zinc lead barite deposit ireland fluid inclusion and stable isotope evidence the silvermines zinc lead barite deposit occurs adjacent to a major normal fault system within a sequence of mississippian tournaisian sandstones shales limestones and dolomites it comprises large synsedimentary syndiagenetic and smaller underlying epigenetic orebodies fluid inclusions within the epigenetic minerals are dominated by a simple liquid vapor type which in places contains one to five solid phases the commonest of which is calcite single phase liquid inclusions are commonest in barite single phase vapor and vapor liquid inclusions are occasionally found in quartz barite and carbonates although there is no indication of extensive boiling fluid inclusion salinities range from 8 to 28 equiv wt percent nacl with modes at 14 and 19 wt percent leachate studies show the fluids to have high sodium concentrations with lesser variable amounts of potassium and calcium and uniformly low magnesium concentrations k na 0 03 0 23 ca na 0 03 0 28 mg ca 0 1 0 67 fluid inclusions within synsedimentary syndiagenetic barite are highly saline indicating the possible presence of a brine pool at the site of ore deposition homogenization temperatures range from 50 degrees to 260 degrees c with most between 140 degrees and 220 degrees c there is a mode at 190 degrees c and a subsidiary group at 140 degrees c required pressure corrections are less than 5 degrees c if the pressure within the epigenetic ore zones was purely hydrostatic as is reasonable a minimum seawater depth of approximately 80 m is required to prevent boiling of some fluids for the whole deposit there is a negative correlation between homogenization temperature and salinity for quartz hosted inclusions which is interpreted as the involvement of two or possibly three fluids in the mineralizing process we suggest that high temperature 8 to 12 equiv wt percent nacl fluids mixed with lower temperature 18 to 22 equiv wt percent nacl fluids both within and below the ore zone during mineralization fluid inclusion waters have delta d values of 24 to 49 per mil for quartz 23 to 29 per mil for dolomite 41 to 55 per mil for barite 46 per mil for sphalerite and 58 per mil for galena the delta 18 o values of the mineralizing fluids calculated from mineral values range from 1 1 to 7 7 per mil for quartz and 1 8 to 5 7 per mil for dolomite these data best represent aqueous fluids that have equilibrated with the geosynclinal sequence and granites underlying the deposit they also suggest that local carboniferous surface and ground waters may have contained a deuterium depleted meteoric component the fluid inclusion evidence presented refutes a model involving the expulsion of carboniferous formation waters and indicates little if any involvement of magmatic waters the geologic geochemical and fluid inclusion evidence best fits a model involving the convection of carboniferous surface waters in the putative thick geosynclinal sequence and associated granitoids below the deposit with a contribution from lower paleozoic formation waters mineral precipitation resulted from fluid mixing in the ore zone with some contribution from carbonate wall rock reactions and possibly boiling

how well can we simulate complex hydro geomorphic process chains the 2012 multi lake outburst flood in the santa cruz valley cordillera blanca peru changing high mountain environments are characterized by destabilizing ice rock or debris slopes connected to evolving glacial lakes such configurations may lead to potentially devastating sequences of mass movements process chains or cascades computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses the present study explores the potential of the novel computational tool r avaflow for simulating complex process chains r avaflow employs an enhanced version of the pudasaini 2012 general two phase mass flow model allowing consideration of the interactions between solid and fluid components of the flow we back calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi lake outburst flood in the artizon and santa cruz valleys cordillera blanca peru involving four lakes and a substantial amount of entrained debris along the path the documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy however small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies but particularly on the development of appropriate strategies for decision making based on uncertain simulation results 2017 the authors earth surface processes and landforms published by john wiley sons ltd

life history of mobile troughs in the upper westerlies abstract increasing evidence indicates that surface cyclogenesis is predominantly a response to the approach of a preexisting trough at upper levels a question then arises about the origin of the upper level predecessor as an initial approach to this question mobile troughs in the major band of westerlies were crudely tracked in daily northern hemispheric 500 mb analysis during nine recent cold seasons these troughs were identified only in the 552 dam height contour between 8 and 15 of them were present on a given day study of a particular cold season showed a median duration of 12 days and a mode of 5 days average zonal phase speed was 13 m s 1 locations or origin and termination of individual troughs were distributed over all longitudes but births greatly exceeded deaths over and east of the rocky mountains in north america and the highlands of central asia trough terminations dominated over the eastern portions of the oceans within the quasi steady planetary waves origins and terminations o

upper level frontogenesis associated with the birth of mobile troughs in northwesterly flow previous studies have shown that 500 hpa mobile trough births or genesis occur preferentially in northwesterly flow during upper level frontogenesis and that cold advection assists in and is a product of mobile trough intensification this study focuses on the synoptic environments and thermal advection patterns of upperlevel fronts associated with mobile trough births in northwesterly flow a climatology of 186 such events derived from an earlier study by sanders shows that most births tend to occur within uniform or diffluent flow and that most tend to be associated with relatively weaker 500 hpa thermal advection most mobile trough births in diffluence however tend to be associated with increasing 500 hpa cold advection typically indicated by a cyclonic rotation of isentropes whereas most mobile trough births in confluence tend to be associated with weaker 500 hpa thermal advection two cases of upper level frontogenesis associated with mobile trough genesis one in diffluence and one in confluence are compared to determine the processes acting to produce the differing thermal advection patterns at 500 hpa a thermal advection tendency equation is developed and shows that the magnitude of the temperature advection can be changed by accelerating the advecting wind speed or by changing the temperature gradient i e vector frontogenesis the latter can be accomplished either by changing the magnitude of the temperature gradient the frontogenetical component fn also known as scalar frontogenesis or by rotating the direction of the temperature gradient relative to the flow the rotational component fs the dominant processes acting on fn for the diffluence and confluence cases are tilting and deformation frontogenesis respectively the dominant process acting on fs for the diffluence case is rotation of the isentropes due to the vorticity term whereas rotation of the isentropes due to the vorticity and tilting terms are both important for the confluence case the rotational component of frontogenesis is cyclonic downstream of the vorticity maximum for both cases favoring increasing cold advection downstream of the vorticity maximum for both cases the rate of rotation of the isentropes at a point due to horizontal advection is large and that due to vertical advection is negligible since advection can only transport the existing isentrope angle and cannot change the isentrope angle the rotational component of frontogenesis normalized by the temperature gradient is the only term that can increase the isentrope angle following the flow this term dominates in the diffluence case but is small in the confluence case this diagnosis suggests the following reasoning in diffluent flow the vorticity associated with the incipient trough is compacted into a more circular shape and intensifies the potent vorticity maximum leads to robust isentrope rotation in confluent flow however the vorticity is deformed into an elongated maximum inhibiting both strong isentrope rotation and increasing cold advection thus the rotational frontogenesis component explains the rotation of the isentropes that is responsible for the differing thermal advection patterns diagnosis of these cases supports the results from the climatology indicating a strong relationship between the synoptic environment and the upper tropospheric thermal advection pattern nevertheless current conceptual models of upper level frontogenesis do not fully explain the variety of these features in the real atmosphere in particular mobile trough genesis and its associated upper level frontogenesis can occur in weak 500 hpa thermaladvection patterns in contrast to the confluence and cold advection that have been previously identified as important to upper level frontal intensification this result provides further support for the possibility that generation and intensification of mobile troughs can occur by barotropic processes

the freezing level in the tropical andes peru an indicator for present and future glacier extents along with air temperatures the freezing level height flh has risen over the last decades the mass balance of tropical glaciers in peru is highly sensitive to a rise in the flh mainly due to a decrease in accumulation and increase of energy for ablation caused by reduced albedo knowledge of future changes in the flh is thus crucial to estimating changes in glacier extents since in situ data are scarce at altitudes where glaciers exist above 4800 m above sea level asl reliable flh estimates must be derived from multiple data types here we assessed the flhs and their spatiotemporal variability as well as the related snow rain transition in the two largest glacier covered regions in peru by combining data from two climate reanalysis products tropical rainfall measuring mission trmm precipitation radar bright band data micro rain radar data and meteorological ground station measurements the mean annual flh lies at 4900 and 5010 m asl for the cordillera blanca and vilcanota respectively during the wet season the flh in the cordillera vilcanota lies 150 m higher compared to the cordillera blanca which is in line with the higher glacier terminus elevations coupled model intercomparison project version 5 cmip5 climate model projections reveal that by the end of the 21st century the flh will rise by 230 m 190 m for representative concentration pathway rcp 2 6 and 850 m 390 m for rcp8 5 even under the most optimistic scenario glaciers may continue shrinking considerably assuming a close relation between flh and glacier extents under the most pessimistic scenario glaciers may only remain at the highest summits above approximately 5800 m asl

barotropic regeneration of upper level synoptic disturbances in different configurations of the zonal weather regime abstract barotropic dynamics of upper tropospheric midlatitude disturbances evolving in different configurations of the zonal weather regime i e in different zonal like large scale flows were studied using observational analyses and barotropic model experiments the contraction stage of upper level disturbances that follows their elongation stage leads to an increase of eddy kinetic energy that is called the barotropic regeneration process in this text this barotropic mechanism is studied through notions of barotropic critical regions btcrs and effective deformation that have been introduced in a previous paper the effective deformation field is equal to the difference between the square of the large scale deformation magnitude and the square of the large scale vorticity regions where the effective deformation is positive correspond to regions where the large scale flow tends to strongly stretch synoptic disturbances a btcr is an area separating two large scale regions of positive effective defo

structural and paleotopographic controls of lead zinc mineralization in the silvermines orebodies republic of ireland occurrence in lower carboniferous and devonian strata in northern tipperary the deposits comprise lower discordant zones deposited epigenetically along the channelways of the ascending ore solutions and upper late tournaisian stratiform syngenetic syndiagenetic zones of sedimentary exhalative origin mineralization occurs in a variety of sediments whose composition reflects the nature of the exhaled fluids and the variable physiochemical conditions in their depositional sites as a result of periodic tectonism on the fault zone these mineralized sediments were subjected to varying degrees of brecciation in a very unstable depositional environment the stratiform deposits of silvermines are synsedimentary products of the exhalation of mineralizing fluids from northwest trending feeder zones on to a late tournaisian sea floor of highly irregular paleotopography modified journal abstract

a five year radar based climatology of tropopause folds and deep convection over wales united kingdom abstracta five year 2006 10 radar based climatology of tropopause folds and convective storms was constructed for wales united kingdom to determine how deep moist convection is modulated by tropopause folds based on the continuous high resolution data from a very high frequency vhf wind profiling radar located at capel dewi wales 183 tropopause folds were identified tropopause folds were most frequent in january with a secondary maximum in july based on data from the u k weather radar network a climatology of 685 convective storms was developed the occurrence of convective storms was relatively high year round except for an abrupt minimum in february april multicellular lines 43 5 were the most common morphology with a maximum in october followed by isolated cells 33 1 with a maximum in may september and nonlinear clusters 23 4 with a maximum in november january convective storms were associated with 104 56 8 of the tropopause folds identified in this study with the associ

70 years of lake evolution and glacial lake outburst floods in the cordillera blanca peru and implications for the future climate change glacier retreat and glacial lake outburst floods glofs are intertwined the cordillera blanca in peru has one of the world s longest glof records and here we assess the evolution of glacial lakes in the region between 1948 and 2017 and investigate the links to documented glofs we also model future lake evolution under two climate scenarios to provide an assessment of current and future glof triggering potential our analysis shows that the number of lakes as well as the total lake area has increased during the historical period the formation of new lakes is however not uniform among different lake types with bedrock dammed lakes exhibiting the largest increase in recent decades we argue that moraine dammed lakes have already formed at the majority of potential locations in the cordillera blanca and that the next generation of lakes which are expected to form in response to glacier retreat over topographically suitable areas will be predominantly bedrock dammed based on a regional glof inventory we show that the peak frequency of glofs occurred from the late 1930s to early 1950s while glofs originating from moraine dammed lakes dominated in this period recent glofs have originated from bedrock dammed lakes at the same time the majority of glofs originated from lakes in a proglacial phase i e in contact with glacier even though the share of proglacial lakes did not exceed 12 at any time step during the analysed period while many moraine dammed lakes evolved into the glacier detached evolutionary phase bedrock dammed lakes became a major lake dam type among proglacial lakes over the remainder of the 21st century a further increase in lake area of up to 10 is anticipated with up to 50 new bedrock dammed lakes likely to develop as glaciers retreat there is little difference in lake development and glof triggering potential under climate scenarios driven by rcp 2 6 and 8 5 based on topographic disposition recent and future lakes do not individually appear more or less susceptible to landslide impact than lakes that already developed earlier in the 20th century synthesizing these findings we forecast that bedrock dammed lakes will become the dominant source of glofs in the next decades because such dams are inherently more stable we expect overall lower glof magnitudes compared to documented glofs from moraine dammed lakes

timing of mineralization at the navan zn pb deposit a post arundian age for irish mineralization navan is the largest of the irish zn pb deposits and contains some of the most important evidence for the inferred early timing of mineralization in ireland clasts of ore above a middle carboniferous erosion surface we have examined diagenetic fabrics within the main ore pale beds and the overlying erosion surface boulder conglomerate in order to determine the timing of mineralization this diagenetic analysis and particularly the presence of premineralization dolomite in the boulder conglomerate has revealed that all of the mineralization postdates the erosion surface and therefore must be post arundian 345 ma in age furthermore the navan mineralization must be entirely epigenetic in origin i e similar to mississippi valley type deposits and is likely to be holkerian 343 ma in age or younger this conclusion disagrees with the previous model of at least partially syngenetic mineralization and has important implications for the age of other deposits in ireland and the nature of irish type deposits in general

on air motion trajectories in cold fronts abstract we examine air parcel trajectories in the two dimensional model for a cold front by reeder and smith these are found to be in close agreement with trajectories deduced from analyses of summertime cool changes in southeastern australia adding further support to the applicability of the numerical model to this kind of cold front the favorable comparison points also to the dynamical consistency of the conceptual model for the cool change which has evolved from the analysis of data from observational experiments

an analysis of frontogenesis in numerical simulations of baroclinic waves abstract using a primitive equation pe model we revisit two canonical flows that were previously studied using a semigeostrophic equation sg model in a previous paper the authors showed that the pe and the sg models can have significantly different versions of the large scale dynamics here they report on the implications of this difference for frontogenesis the program for the study of frontogenesis developed by b j hoskins and collaborators is followed to show how in the pe version of the canonical cases the surface warm front develops before the cold front and why the upper level front is a long nearly continuous feature going from ridge to trough the frontogenesis experienced by an air parcel is computed following the parcel to illustrate better the mechanisms involved as the present calculations are carried out longer than most previous ones the relation of the upper frontogenesis to the formation of the upper level cutoff cyclone is also examined trajectory and three dimensional g

piecewise tendency diagnosis of dynamical processes governing the development of an upper tropospheric mobile trough abstract the intensification and evolution of midlatitude upper tropospheric mobile troughs may be viewed in terms of the isentropic advection and deformation of the tropopause potential vorticity gradient the potential vorticity viewpoint allows one to qualitatively assess observed events in the context of existing theories of mobile trough genesis such as baroclinic instability or downstream development in order to quantitatively determine the role of distinct dynamical process the method of piecewise tendency diagnosis or ptd is developed ptd is an extension of piecewise potential vorticity inversion applied to height tendencies with the forcing terms in the quasigeostrophic height tendency equation partitioned into potential vorticity advection associated with distinct dynamical processes a particular case of mobile trough genesis which occurred during 1 4 december 1980 over north america is diagnosed using ptd although about 20 of the intensification of the trough was due to superposition

recent climatic change and catastrophic geomorphic processes in mountain environments climatic warming during the last 100 150 years has resulted in a significant glacier ice loss from mountainous areas of the world certain natural processes which pose hazards to people and development in these areas have accelerated as a result of this recent deglaciation these include glacier avalanches landslides and slope instability caused by glacier debuttressing and outburst floods from moraine and glacier dammed lakes in addition changes in sediment and water supply induced by climatic warming and glacier retreat have altered channel and floodplain patterns of rivers draining high mountain ranges the perturbation of natural processes operating in mountain environments caused by recent climatic warming ranges from tens of decades for moraine dam failures to hundreds of years or more for landslides the recognition that climatic change as modest as that of the last century can perturb natural alpine processes has important implications for hazard assessment and future development in mountains even so these effects are probably at least an order of magnitude smaller than those associated with late pleistocene deglaciation ca 15 000 to 10 000 years ago

conceptual models of upper level frontogenesis in south westerly and north westerly flow the conceptual model proposed by shapiro as it is applied to the evolution of an upper level frontal zone within a baroclinic wave is reviewed and its limitations are investigated through previous literature and two casestudies presented in this paper the early stages in the evolutions of these two cases are used to examine specific limitations of this conceptual model 1 upper level frontogenesis in south westerly flow that evolves from a state of equivalent barotropy to a state of cold advection along the front and 2 upper level frontogenesis in northwesterly flow with along front variation in the sign of the thermal advection such that warm advection occurs upstream of cold advection in the thermal trough vector frontogenesis diagnostics for the lagrangian rate of change of the magnitude and direction of the horizontal potential temperature gradient including tilting due to vertical motion are derived these diagnostics are applied to the two cases to examine the maintenance of the potential temperature gradient and the development of cold advection along each upper level front the upper level front in south westerly north westerly flow was maintained primarily by deformation tilting frontogenesis in agreement with previous research the increasing cold advection along the upper level front in both cases was related to an upstream vorticity maximum for the case in south westerly flow the pre existing vorticity maximum approached a downstream equivalent barotropic upper level front in a manner similar to an instant occlusion resulting in cold advection along the length of the upper level front for the case in north westerly flow an intensifying vorticity maximum concentrated the cold advection in the base of the thermal trough as warm advection developed upstream these two cases are compared to upper level fronts in previous literature and a climatology of upper level fronts associated with landfalling cyclones over the eastern north pacific ocean the results indicate that these two cases are typical of early evolutions of upper level fronts that can occur in south westerly and north westerly flow therefore a revised version of the shapiro conceptual model is presented that represents more accurately the early evolutions exhibited in the present and previous studies

comments on the influence of rotational frontogenesis and its associated shearwise vertical motions on the development of an upper level front by a a lang and j e martin january a 2010 136 239 252 two previous studies by rotunno et al 1994 j atmos sci 51 3373 3398 and schultz and doswell 1999 q j r meteorol soc 125 2535 2562 offer conflicting views on the origin of geostrophic cold air advection that is sometimes present during upper level frontogenesis although lang and martin 2010 claim to reconcile these two studies this comment offers four reasons why reconciliation is not possible first the necessary calculations to compare the tilting frontogenesis term to the horizontal frontogenesis terms are not performed second the thermal advection tendency or isentrope orientation tendency in the region of the developing cold air advection is not calculated third previous studies showing that the vertical terms in these diagnostics are likely associated with warm air advection not cold air advection are not disproven this fact also may explain the predominance of relatively weak geostrophic thermal advection in climatologies of upper level fronts fourth concerns are raised about some of the statements made in lang and martin 2010 these comments also fix an error in eq 11 in schultz and doswell 1999 copyright 2012 royal meteorological society

bacteria were responsible for the magnitude of the world class hydrothermal base metal sulfide orebody at navan ireland we report sulfur and lead isotope analyses of mine concentrates from navan the largest zinc deposit in ireland these samples each representing up to a million tonnes of ore show very limited isotopic variation with mean 34 s 13 6 2 per mil n 20 and galena concentrate mean 206 pb 204 pb 18 19 0 03 n 7 calculations suggest 90 percent of the navan sulfides were derived through bacteriogenic reduction of mississippian seawater sulfate whereas metals were acquired from a local orogenic crustal source beneath the orebody enhanced bacterial activity was fundamental to ore deposition at navan no bacteria no giant ore deposit

the influence of rotational frontogenesis and its associated shearwise vertical motions on the development of an upper level front the total quasi geostrophic qg vertical motion is partitioned into transverse and shearwise couplets oriented parallel to and along the geostrophic vertical shear respectively in order to examine the role of rotational frontogenesis and its associated shearwise circulation in the life cycle of an upper front jet system in northwesterly flow in particular the analysis emphasizes two aspects of that role 1 the influence of shearwise on scalar frontogenesis and 2 the effect of rotational frontogenesis and its associated vertical circulation on the initiation of along flow cold air advection during upper frontogenesis the case study analysis reveals that shearwise subsidence persistently and significantly contributes to scalar frontogenesis throughout the life cycle the transverse subsidence contribution to scalar frontogenesis is initially weak but grows more substantial after the establishment of along flow cold air advection near the base of the thermal trough prior work has argued that the development of along flow cold air advection arises from a cyclonic rotation of promoted either by contributions from tilting or horizontal kinematics from the qg perspective adopted in the present study the tilting and kinematic rotations are seen as interconnected aspects of a single underlying dynamical process rotational frontogenesis in which the rotation of produced by vertical vorticity is accompanied by a discrete vertical circulation the shearwise circulation that provides the subsidence upshear of the vorticity maximum required to initiate along flow cold air advection it is further suggested that the characteristic distribution of the kinematic and tilting contributions to rotation of in the vicinity of an upper tropospheric vorticity maximum underlies the observed preference for the development of upper level fronts in northwesterly flow copyright 2010 royal meteorological society

origin of a giant orebody at navan ireland the navan base metal deposit in ireland formed 360 myr ago1 and is one of the world s largest orebodies with 70 million tonnes of 12 zn pb much of the mineralization was sedimentary exhalative other well known examples of this class of the so called sedex deposits are mount isa in australia sullivan in canada and meggen in germany several models for the formation of such deposits have been suggested here we report the first systematic stratigraphic pb isotopic study of galenas in any giant exhalative zn pb orebody we document evidence that the sources of pb in the navan orebody evolved to produce increased dispersion and less radiogenic averages of lead isotopic compositions this is as expected if the orebody formed from a hydrothermal convection cell which expanded to scavenge metals from progressively deeper parts of the continental crust

preliminary sulphur isotope data of diagenetic and vein sulphides in the lower palaeozoic strata of ireland and southern scotland implications for zn pb ba mineralization genetic models for many irish lower carboniferous zn pb ore deposits invoke a dual supply of sulphide the dominant source is from the bacteriogenic reduction of lower carboniferous seawater sulphate but a significant minor supply is derived from deep seated sources the 34 s range of the latter component varies among the deposits from the lightest range of 15 to 0 at keel to the heaviest of 4 to 14 4 in the navan tatestown area we hypothesize that such sulphur is leached mainly from diagenetic sulphide minerals in the underlying lower palaeozoic sediments 6 s of pyrite in the silurian ordovician moffat shales 17 1 to 0 6 and of sphalerite and galena in lower palaeozoic hosted veins at salterstown 8 7 to 4 5 and wanlockhead 10 3 to 5 1 are consistent with the hypothesis below the navan ore deposit lower palaeozoic shales containing minor diagenetic pyrite with a very wide range in 34 s have been found 34 s is typically heavy 16 but extreme values up to 62 are encountered the general enrichment in 34 s is in accord with the noticeably heavy isotopic composition of deep seated sulphur in the navan orebody and its tatestown satellite our preliminary results therefore suggest that geographical variations in the 34 s range of lower palaeozoic diagenetic write may have contributed to the isotopic variation in the deep seated sulphur among the irish deposits

regional synthesis of last glacial maximum snowlines in the tropical andes south america the modern glaciers of the tropical andes are a small remnant of the ice that occupied the mountain chain during past glacial periods estimates of local last glacial maximum lgm snowline depression range from low e g 200 300 m in the junin region peru through intermediate 600 m at laguna kollpa kkota in bolivia to high e g 1100 1350 m in the cordillera oriental peru although a considerable body of work on paleosnowlines exists for the tropical andes absolute dating is lacking for most sites moraines that have been reliably dated to 21 cal kyr bp have been identified at few locations in the tropical andes more commonly but still rarely moraines can be bracketed between about 10 14 c kyr 11 5 cal kyr bp and 30 14 c kyr bp typically only minimum limiting ages for glacial retreat are available cosmogenic dating of erratics on moraines may be able to provide absolute dating with sufficient accuracy to identify deposits of the local lgm ongoing work using cosmogenic 10 be and 26 al in peru and bolivia suggests that the local lgm may have occurred prior to 21 cal kyr bp r 2005 elsevier ltd and inqua all rights reserved

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

geomorphologically effective floods from moraine dammed lakes in the cordillera blanca peru abstract outburst floods originating in moraine dammed lakes represent a significant geomorphological process as well as a specific type of threat for local communities in the cordillera blanca peru 8 5 10 s 77 78 w an exceptional concentration of catastrophic floods has been reported from the cordillera blanca in the first half of 20th century 1930s 1950s leading to thousands of fatalities the main objective of this paper is to provide a revised and comprehensive overview of geomorphologically effective floods in the area of interest using various documentary data sources verified by analysis of remotely sensed images 1948 2013 and enhanced by original field data verified events n 28 4 not mentioned before are analysed from the perspective of spatiotemporal distribution pre flood conditions causes mechanisms and geomorphological impacts as well as socioeconomical consequences revealing certain patterns and similar features glofs are further classified according to their magnitude 5 extreme events 8 major events and 15 minor events are distinguished referring to the quantified geomorphological and socioeconomical impacts selected moraine dams and flood deposits are dated using lichenometric dating special attention is given to moraine dam breaches the most frequent type of water release with the most significant consequences selected major events and their consequences are studied in detail in a separate section finally a general schematic model of lake formation growth and post flood evolution reflecting initial topographical setting and glacier retreat is introduced and the utilization of the obtained results is outlined

formation of fossil hydrothermal chimneys and mounds from silvermines ireland sulphur isotope analyses reveal that the fossil hydrothermal pyrite mound and tubes at silvermines were produced by the reaction of hydrothermal fe ii with bacteriogenically reduced sulphur species 34s range 18 4 to 42 5 this took place in a brine pool dominated by hyper saline carboniferous seawater this is in contrast to their modern but considerably larger morphological counterparts forming by direct precipitation of hydrothermal sulphides on the east pacific rise at 21 n

composite synoptic scale environments conducive to north american polar subtropical jet superposition events abstracta polar subtropical jet superposition represents a dynamical and thermodynamic environment conducive to the production of high impact weather prior work indicates that the synoptic scale e

regional fluid flow and the genesis of irish carboniferous base metal deposits the irish carbonate hosted base metal deposits have long been an enigmatic subclass of deposit some of the irish deposits harberton bridge allenwood are clearly epigenetic hosted in breccia pipes and have close affinities to mississippi valley type deposits others are characterised by stratabound and sometimes stratiform mineralisation abbeytown navan while a third group is associated closely with concordant dolomitic breccias and cavity fill mineralisation at the base of carbonate mud mounds lisheen ballinalack when the stratigraphic and textural evidence is reviewed it is apparent that all of the base metal mineralisation occurred in already compacted sediments hence mineralisation probably occurred at depths of at least several 100 m depth below the sea bed the mineralisation occurred either during transtensional lower carboniferous basin development or subsequently during the onset of variscan shortening fluids may have been derived from dewatering of variscan driven deformation to the south of the carbonate platform with fluid flow through major fracture zones and basal clastic aquifers alternatively high heat flow produced by lower carboniferous extension may have driven the mineralising system syn genetic models are extremely difficult to sustain

ore depositional process in the navan zn pb deposit ireland the navan zn pb deposit in ireland is hosted by a lower carboniferous carbonate dominated sedimentary sequence in excess of 97 percent of the ore is hosted by a courceyan shallow water succession termed the pale beds the ore occurs as complex strata bound tabular lenses often dislocated by faulting and truncated by a submarine erosional slide structure above this surface unconformity lies the economically minor but genetically important conglomerate group ore hosted by a complex debris flow termed the boulder conglomerate timing constraints on the mineralization can be defined by the relationship to the erosion surface and style of mineralization suggesting a late chadian or early arundian age approximately 345 ma the bulk of the ore formed below the erosion surface in the semilithified to lithified pale beds ore the mineralogy of the economic ores is relatively simple being dominated by sphalerite and galena in a 5 1 ratio pyrite and marcasite are present in subordinate amounts in the majority of the pale beds ore but dominate the conglomerate group ore and the pale beds ore immediately below the erosion surface particularly lens 2 1 gangue minerals are dominated by calcite dolomite and barite the morphology of the mineralization reflects subsea floor emplacement the orebody occurs as numerous strata bound horizons ranging from intense high grade massive sulfides to lower grade sulfide layers separated by barren limestone in all cases there is strong evidence for tectonic disruption during ore deposition sulfides were dominantly deposited as open space growth and replacement of host rock open space textures include dendritic skeletal stalactitic internal sediment geopetal and coarse bladed forms the general absence of coarse euhedral cavity lining textures or substantial collapse brecciation suggests that large cavities were not present prior to mineralization replacement textures range from delicate pseudomorphs of biodasts to more destructive granular styles sulfide sulfur isotope analyses exhibit two dominant groupings of delta 34 s from around 23 to 5 and 0 to 15 per mil respectively and a third minor grouping around 32 to 28 per mil at least two sources of sulfur are invoked values around 23 to 15 per mil are considered to be the result of bacteriogenic reduction of lower carboniferous seawater sulfate approximately 20ppm with a characteristic fractionation around 35 to 45 per mil away from sulfate this is the most common range of delta 34 s in the deposit values around 8 to 15 per mil are interpreted to be hydrothermal sulfide transported with the metal bearing fluid mixing of these two components is inferred from the isotopic data and trends in the mineral paragenesis barite has a mean of delta 34 s 21 or 2 per mil which falls within the range generally recognized for lower carboniferous seawater sulfate we consider that contemporaneous seawater sulfate was the dominant source of sulfur in the barite at navan implying that seawater accessed the pale beds at the time of mineralization

a potential vorticity diagnostic approach to upper level frontogenesis within a developing baroclinic wave the process of tropopause folding is studied in the context of the life cycle of baroclinic waves previous studies of upper level frontogenesis have emphasized the role of the vertical circulation in driving stratospheric air down into the midtroposphere here a potential vorticity based approach is adopted that focuses on the generation of a folded tropopause to facilitate comparison of the two approaches the diagnosis is applied to the upper level front previously simulated and studied by rotunno et al the potential vorticity approach clarifies the primary role played by the horizontal nondivergent wind in producing a fold and explains why folding should be a common aspect of baroclinic development between the trough and upstream ridge prolonged subsidence within a region of weak system relative flow generates a tropopause depression oriented at an angle to the large scale flow the large scale vertical shear then locally increases the slope of the tropopause eventually leading to a tropopause fold in contrast tropopause folding in the base of the trough is caused by the nondivergent cyclonic circulation associated with the surface thermal wave the winds associated with the thermal wave amplify the potential vorticity wave aloft and these winds which decrease with height rapidly generate a tropopause fold within the trough

a fossil hydrothermal worm assemblage from the tynagh lead zinc deposit in ireland fossil hydrothermal chimneys were first discovered at silvermines1 ireland subsequent discoveries of fossils associated with mounds and chimneys in sulphide deposits within the ophiolite complexes of cyprus2 and oman3 prove that life forms similar to those colonising active vents on the east pacific rise4 7 were extant 100 myr ago around ridge crest hot springs here i report the discovery of 350 myr old worm like fossils recovered from pyrite chimneys associated with sedimentary exhalative mineralization at tynagh ireland this find suggests that even older examples of life existing at seafloor hot springs may be awaiting discovery

initiation and evolution of an intense upper level front abstract within confluent northwesterly flow of an intensifying baroclinic wave over north america in late october 1963 an intense frontal zone developed in 12 h near the inflection point in the middle and upper troposphere by 24 h after its initial appearance the zone extended roughly from 400 to 700 mb and from the inflection point to just beyond the downstream trough horizontal gradients of potential temperature reached 15 20 k 100 km 1 air within the frontal zone was extremely dry as the accompanying trough approached the east coast of he united states surface frontogenesis occurred offshore remaining distinct from the upper level front a region of subsidence elongated in the direction of the upper level flow displayed maximum descent on the warm edge of the frontal zone and played a frontogenetical role through tilting of the isentropic surfaces analysis of isentropic potential vorticity showed significant increase of this quantity near the cold base and a probable decrease near the top