analysis of lake ice dynamics and morphology on lake el gygytgyn ne siberia using synthetic aperture radar sar and landsat 1 a time series of more than 450 combined ers 2 radarsat 1 and landsat 7 scenes acquired between 1998 and 2001 was analyzed to develop a fairly complete picture of lake ice dynamics on lake el gygytgyn ne siberia 67 5 n 172 e this 14 km3 lake partially fills a meteorite impact crater formed 3 6 million years ago and is home to a paleoenvironmental coring project the duration of lake ice cover and the onset of lake ice breakup are important both to interpretations of the archived sediment core record and to future drilling projects that will use the ice as a stable platform ice formation snowmelt and ice breakup likely occur in late october mid may and early july respectively these data were used to validate a one dimensional energy balance lake ice model which can now be used to hindcast paleoclimate based on core proxy information synthetic aperture radar sar backscatter from the lake ice also revealed unusual spatial variations in bubble content which were found to indicate the level of biological productivity in the sediments directly beneath the ice with the highest productivity located in the shallowest 0 10 m as well as the deepest 170 175 m regions of the lake seismic data indicates that the backscatter anomaly above the deepest water is collocated with the central peak of the impact crater 500 m below the surface several hypotheses are presented to explain this anomaly regardless of cause the fact that large spatial variations in biological productivity exist in the lake has important implications for selecting the locations of future sediment cores

structural and stratigraphie features and ers 1 synthetic aperture radar backscatter characteristics of ice growing on shallow lakes in nw alaska winter 1991 1992 changes in ers 1 c band synthetic aperture radar sar backscatter intensity from ice growing on shallow tundra lakes at three locations in nw alaska are described ice core analysis shows that at all lakes on the coast at barrow the ice whether floating or frozen to the bottom includes an inclusion free layer overlying a layer of ice with tubular bubbles oriented parallel to the direction of growth the clear ice may also be overlain by a discontinuous layer of bubbly snow ice backscatter is low 16 to 22 db at the time of initial ice formation probably due to the specular nature of the upper and lower ice surfaces causing the radar pulse to be reflected away from the radar as the ice thickens during the autumn backscatter rises steadily once the ice freezes to the lake bottom regardless of the presence of forward scattering tubular bubbles low backscatter values of 17 to 18 db are caused by absorption of the radar signal in the lake bed for ice that remains afloat all winter the ice water interface and the tubular bubbles combine presumably via an incoherent double bounce mechanism to cause maximum backscatter values of the order of 6 to 7 db the saturates at 6 to 7 db before maximum ice thickness and tubular bubble content are attained a simple ice growth model suggests that the layer of ice with tubular bubbles need be only a few centimeters thick midway through the growth season to cause maximum backscatter from floating ice during the spring thaw a previously unreported backscatter reversal is observed on the floating and grounded portions of the coastal lakes but not on the lakes farther inland this reversal may be related to the ice surface topography and wetness plus the effects of a longer cooler melt period by the coast time series of backscatter variations from shallow tundra lakes are a record of 1 the development of tubular bubbles in the ice and by association changes in the gas content of the underlying water and 2 the freezing of ice to the bottoms of the lakes and therefore lake bathymetry and water availability sar is also able to detect the onset of lake ice growth in autumn and the initiation of the spring thaw and thus has potential for monitoring high latitude lake ice growth and decay processes in relation to climate variability

radiation damage halos in quartz radiation damage halos are present in quartz that surrounds or is adjacent to accessory minerals such as zircon these halos are not visible in transmitted light but are revealed by cathodoluminescence cl they extend up to 45 m away from the source of radioactivity some halos show concentric rings similar to those previously reported in pleochroic halos in biotite radiation damage halos occur in three main settings surrounding inclusions within quartz grains penetrating into quartz from adjacent radionuclide bearing grains and in quartz cement near such grains halos are more common in pre paleozoic rocks than in younger rocks except in cases of unusual enrichment in radioactive elements halos result from damage to quartz crystal structure identical to the process forming pleochroic halos in biotite damage is caused by alpha particles emitted by radioactive elements within mineral grains and is a partial function of time consequently radiation damage halos may have potential uses in geochronology

an evaluation of volcanic cloud detection techniques during recent significant eruptions in the western ring of fire we examined recent volcanic cloud events in the western pacific and indonesian area to validate the performance of remote sensing techniques used to support the international airways volcano watch iavw five events were considered during which eruptions from eight volcanoes injected ash into the upper troposphere or lower stratosphere for one of the eruptions at miyakejima japan at least five aircraft encountered volcanic ash clouds and the cost to three operators alone exceeded us 12 000 000 in aircraft repairs diversions and lost operating time we performed reverse absorption and pattern analysis using gms 5 vissr modis and avhrr data and we examined toms so2 and aerosol index data surface based observations pilot reports and dispersion model output our results verify that the introduction of reverse absorption using the geostationary gms 5 platform significantly enhanced our capacity to monitor volcanic ash clouds in the region in one case we tracked an eruption cloud for approximately 80 h the primary impediment to remote monitoring is the presence of overlying cloud or substantial amounts of ice within the volcanic clouds toms data showed success in identifying volcanic clouds during these conditions but was limited by the infrequency of observations more effective future operation of the iavw relies on developing complementary methods of volcanic cloud remote sensing and greatly increasing the amount and quality of available surface and air observations including observations of precursor activity an understanding of the likely future limitations of remote sensing techniques will aid in the refining of iavw procedures

origin of compositional layering and mechanism of crustal thickening in the high grade gneiss terrain of sri lanka abstract the highland complex of sri lanka comprises a 7 km thick succession of banded para and orthogneisses at granulite grade or partly retrograded we interpret this complex as a tectonostratigraphic unit in which no primary stratigraphy is preserved this succession with a probable depositional age of 2 ga evolved from a rift basin into a foredeep and then into a fold and thrust belt prior to severe flattening and transport into the lower crust during the final stages of collision some 550 620 ma ago granitoid rocks were emplaced into the supra crustal sequence at various stages of the tectonic evolution between 1950 and 670 ma ago and the original intrusive contacts became obscured or severely modified during progressive non coaxial ductile deformation structures that predate the presently observed layering are preserved in rootless isoclinal folds boudins and microstructures and in deformed pre granulite metamorphic minerals preserved in garnet porphyroblasts the evolution of the highland complex is similar to that of other precambrian granulite terrains notably parts of the grenville province of canada and probably resulted from collisional tectonics during which the original supracrustal assemblage was detached from its archaean to palaeoproterozoic basement the paucity of structures reflecting the early deformational history is due to severe flattening and ductile deformation during predominantly non coaxial deformation when the highland rocks were transported into the lower crust

structure and chemistry of zircon and zircon group minerals zircon zrsio4 is a common accessory mineral in nature occurring in a wide variety of sedimentary igneous and metamorphic rocks known to incorporate an assortment of minor and trace elements zircon has the ability to retain substantial chemical and isotopic information leading to its use in a wide range of geochemical investigations including studies on the evolution of earth s crust and mantle e g hanchar et al 1994 bowring 1995 vervoort et al 1996 hoskin and schaltegger this volume valley this volume as well as age dating e g gibson and ireland 1995 bowring et al 1998 solar et al 1998 bowring and schmitz this volume ireland and williams this volume parrish et al this volume the physical and chemical durability of zircon is a major factor in it being the mineral by which many of earth s oldest known rocks have been dated bowring et al 1989 maas et al 1992 buick et al 1995 bowring and williams 1999 wilde et al 2001 and is also an important factor in zircon being proposed as a candidate waste form for the geologic disposal of excess plutonium from dismantled nuclear weapons ewing and lutze 1997 ewing 1999 burakov et al 2002 burakov et al 2003 ewing et al this volume the chemical and physical properties of zircon and its ability to incorporate and retain trace elements are largely determined by its crystal structure the zircon structure is adopted by numerous minerals and synthetic compounds with the general formula at o4 in which high field strength t site cations occupy isolated tetrahedra and a site cations occupy larger eight coordinated structural sites zircon type compounds share many physical properties as well as displaying variable degrees of solid solution among end members

variability in ice phenology on great bear lake and great slave lake northwest territories canada from seawinds quikscat 2000 2006 abstract the temporal evolution of the backscatter coefficient sigma nought from quikscat was evaluated for monitoring ice phenology on great bear lake 66 n 121 w and great slave lake 61 40 n 114 w northwest territories canada results indicated that from quikscat can be used to detect melt onset water clear of ice and freeze onset dates on both lakes an ice phenology algorithm was then developed to assess the spatiotemporal variability on both lakes from quikscat for the period 2000 2006 results showed that for great slave lake the average melt onset date occurred on year day yd 123 the average water clear of ice date was on yd164 and the average freeze onset date was on yd330 on great bear lake the average melt onset date occurred on yd139 the average water clear of ice date was yd191 and the average freeze onset date was yd321 ice cover remained present for at least five weeks longer on great bear lake than on great slave lake and most of the difference can be explained by earlier ice melt on great slave lake spatially on great bear lake melt onset took place first in the eastern arm water clear of ice occurred first in southeastern and western arms and freeze onset appeared first in the northern arm and along the shorelines on great slave lake melt onset began first in the central basin and then progressed to the northern and eastern arms later in the season the central basin of great slave lake cleared earlier than the periphery due to the discharge from the slave river freeze onset on great slave lake occurred first within the east arm closely followed by the north and west arms and then finally in the centre of the main basin

spatial and temporal patterns in arctic river ice breakup observed with modis and avhrr time series abstract the timing of spring river ice breakup a major annual event for physical biological and human systems on arctic rivers has been used to infer regional climate variations over the past century or more most observations of ice breakup are recorded as point data taken from selected ground based stations it is unknown whether these point observations are fully representative of breakup patterns elsewhere along the course of a river here daily time series of moderate resolution imaging spectroradiometer modis and advanced very high resolution radiometer avhrr satellite images are used to remotely sense spatial and temporal patterns in ice breakup along 1600 3300 km lengths of the lena ob yenisey and mackenzie rivers the first day of predominantly ice free water is visually identified and mapped for ten years 1992 1993 1995 1998 and 2000 2003 with a mean precision of 1 75 days the derived breakup dates show high correlation with ground based observations although a slight trend towards earlier satellite derived dates can be traced to differences in the way ice breakup date is defined large ice jams are often observed particularly at confluences although smaller ice jams may not be visible due to the limited spatial resolution of the imagery used at the watershed scale spatial patterns in breakup seem to be primarily governed by latitude timing of the spring flood wave and location of confluences with major tributaries interestingly channel scale factors such as slope width and radius of curvature which are known to influence ice breakup at the reach scale do not appear to be major factors at the scale observed here the degree of similarity between interannual trends in breakup date at distant points along a river is generally high which supports the use of point scale data to infer regional climate variations this similarity does not hold true for the mackenzie river where substantial spatial differences in breakup trends are observed a new variable spatially integrated breakup date d i uses weighted spatial averaging to provide a more encompassing measure of breakup timing the ob and yenisey rivers show similar trends in spatially integrated breakup date from year to year in contrast the mackenzie and lena show a remarkably consistent negative correlation here attributed to sea surface temperature anomalies associated with the pacific decadal oscillation index

thermal disequilibrium at the top of volcanic clouds and its effect on estimates of the column height satellite images of large volcanic explosions reveal that the tops of volcanic eruption columns are much colder than the surrounding atmosphere1 we propose that this effect occurs whenever a mixture of hot volcanic ash and entrained air ascends sufficiently high into a stably stratified atmosphere although the mixture is initially very hot it expands and cools as the ambient pressure decreases we show that cloud top undercoolings in excess of 20 c may develop in clouds that penetrate the stratosphere this is consistent with observations of the 4 april 1982 eruption of el chichon1 and the 18 may 1980 eruption of mount st helens2 furthermore from our model results we predict that for a given cloud top temperature variations in the initial temperature of 100 200 c may correspond to variations in the column height of 5 10 km we deduce that the present practice of converting satellite based measurements of the temperature at the top of volcanic eruption columns to estimates of the column height will produce rather inaccurate results and should therefore be discontinued

three dimensional volcanic aerosol dispersal a comparison between multiangle imaging spectroradiometer misr data and numerical simulations 1 the three dimensional reconstruction of volcanic plumes is a central goal to enhance our understanding on dispersal processes in this paper we use data from the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft combined with a stereo matching retrieval procedure we show the potential of misr in capturing important features of volcanic plumes like column height optical depth type and shape of the finest particles of two highly explosive eruptions occurring on mount etna in 2001 and 2002 this work tests how tephra dispersal models reconstruct the 3 d shape of volcanic clouds we compare misr data with fall3d an eulerian model for the transport and deposition of volcanic ash and aerosols coupled with the weather research and forecasting mesoscale meteorological model agreement between simulations and misr data is good regarding both events although it could be improved by increasing the accuracy of the meteorological data a better constraint on volcanological input parameters like the height of the eruptive column and improving our understanding of processes such as aggregation phenomena and volcanic cloud microphysics

radiation damage rims in quartz from uranium bearing sandstones abstract using cathodoluminescence cl mode of a scanning electron microscope sem radiation damage in quartz is made visible in uranium vanadium bearing sandstones located in the salt wash member of the morrison formation jurassic from the colorado plateau u s a detrital quartz grains surrounded by uranium minerals display radiation damage rims three concentric rims with thicknesses of 37 m 24 m and 16 m have been observed the rims are similar to halos surrounding uranium and thorium rich accessory minerals observed by owen 1988 they are due to alpha particles which create damage when penetrating a medium the width of the rims agrees well with the bragg kleeman rule and corresponds to the most energetic alpha particles in the 238u decay series sandstones entirely cemented by vanadium clays also exhibit radioactive rims which demonstrates that uranium has been removed during diagenesis these results have important implications for the uranium ore genesis in the salt wash sandstones because they imply an ancient episode of uranium leaching prior to recent weathering therefore cathodoluminescence in sandstones may be useful in recognizing ancient zones or episodes of accumulation and leaching of alpha emitting nuclides from the uranium series

local seismic and infrasound observations of the 2009 explosive eruptions of redoubt volcano alaska article i nfo local seismic and infrasound data are used to characterize the march april 2009 eruptions of redoubt volca no alaska data are from a network of ten seismic stations ranging from 2 6 to 21 km from the vent and a single infrasound sensor 12 2 km from the vent measurements were made for more than 30 explosive erup tions including the 19 numbered events that were identified during the eruption response more than 30 smaller explosions were also identified measured parameters include onset time duration reduced dis placement dr pressure seismic energy and acoustic energy results were compared with complementary gas and lightning data based on ratios of pressure to dr and acoustic to seismic energy we find that the initial group of explosive eruptions on 23 24 march was relatively stronger seismically and included the four highest dr values we infer that these represent vent enlargement or stronger coupling between the magma and wall rocks one event at 12 31 ut on 23 march had an extremely high pressure of 250 pa for the initial pulse and was likely weakly seismically coupled a second group of explosive eruptions on 27 29 march was relatively stronger acoustically deposits were finer grained and of different lithology with less scoria and more dense clasts these two groups may represent different modes of gas release cumulative acoustic energy as a function of time correlates well with comparable lightning and so2 data suggesting that all three provide insight regarding different factors of gas release for the eruption as a whole the number of events identified depends on criteria measured and depends on the goals of the investigations overall the eruptions were substantially stronger than recent eruptions in alaska with some durations exceeding 1 h and pressures an order of magnitude higher

microwave backscatter from arctic lake ice and polarimetric implications polarimetric synthetic aperture radar satellite and ground based ku and x band scatterometer measurements are used to explore the scattering mechanism for ice in shallow arctic lakes wherein strong radiometric responses are seen for floating ice and low returns are evident where the ice has grounded scatterometer measurements confirm that high backscatter is from the ice water interface whereas polarimetric decomposition suggests that the dominant scattering mechanism from that interface is single bounce using fresnel equations a simple model for surface bounce from the ice water interface is proposed and its predictions are supported by experimental parameters such as co pol phase difference co pol ratio and the results of rigorous numerical modeling despite early research suggesting double bounce scattering from columnar air bubbles and the ice water interface as the dominant scattering mechanism in shallow lakes this paper strongly supports a single bounce model

radiation effects in zircon the widespread distribution of zircon in the continental crust its tendency to concentrate trace elements particularly lanthanides and actinides its use in age dating and its resistance to chemical and physical degradation have made zircon the most important accessory mineral in geologic studies because zircon is highly refractory it also has important industrial applications including its use as a lining material in high temperature furnaces however during the past decade zircon has also been proposed for advanced technology applications such as a durable material for the immobilization of plutonium or when modified by ion beam irradiation as an optic waveguide material in all of these applications the change in properties as a function of increasing radiation dose is of critical importance in this chapter we summarize the state of knowledge on the radiation damage accumulation process in zircon

an overview of the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano alaska erupted for the first time since 1990 explosions ejected plumes that disrupted international and domestic airspace sent lahars more than 35 km down the drift river to the coast and resulted in tephra fall on communities over 100 km away geodetic data suggest that magma began to ascend slowly from deep in the crust and reached mid to shallow crustal levels as early as may 2008 heat flux at the volcano during the precursory phase melted 4 of the drift glacier atop redoubt s summit petrologic data indicate the deeply sourced magma low silica andesite temporarily arrested at 9 11 km and or at 4 6 km depth where it encountered and mixed with segregated stored high silica andesite bodies the two magma compositions mixed to form intermediate silica andesite and all three magma types erupted during the earliest 2009 events only intermediate and high silica andesites were produced throughout the explosive and effusive phases of the eruption the explosive phase began with a phreatic explosion followed by a seismic swarm which signaled the start of lava effusion on march 22 shortly prior to the first magmatic explosion early on march 23 2009 utc more than 19 explosions or events were produced over 13 days from a single vent immediately south of the 1989 90 lava domes during that period multiple small pyroclastic density currents flowed primarily to the north and into glacial ravines three major lahars flooded the drift river terminal over 35 km down river on the coast tephra fall deposited on all aspects of the edifice and on several communities north and east of the volcano and at least two and possibly three lava domes were emplaced lightning accompanied almost all the explosions a shift in the eruptive character took place following event 9 on march 27 in terms of infrasound signal onsets the character of repeating earthquakes and the nature of tephra ejecta more than nine additional explosions occurred in the next two days followed by a hiatus in explosive activity between march 29 and april 4 during this hiatus effusion of a lava dome occurred whose growth slowed on or around april 2 the final explosion pulverized the very poorly vesicular dome on april 4 and was immediately followed by the extrusion of the final dome that ceased growing by july 1 2009 and reached 72 m m 3 in bulk volume the dome remains as of this writing effusion of the final dome in the first month produced blocky intermediate to high silica andesite lava which then expanded by means of lava injection beneath a fracturing and annealing cooling surface crust in the first week of may a seismic swarm accompanied extrusion of an intermediate to high silica andesite from the apex of the dome that was highly vesicular and characterized by lower p 2 o 5 content the dome remained stable throughout its growth period likely due to combined factors that include an emptied conduit system steady degassing through coalesced vesicles in the effusing lava and a large crater pit created by the previous explosions we estimate the total volume of erupted material from the 2009 eruption to be between 80 m and 120 m m 3 dense rock equivalent dre the aim of this report is to synthesize the results from various datasets gathered both during the eruption and retrospectively and which are represented by the papers in this publication we therefore provide an overall view of the 2009 eruption and an introduction to this special issue publication

a backscatter modeling for river ice analysis and numerical results a microwave backscatter model was developed to help provide an understanding of the interaction of a radar signal with the different ice types formed on natural freshwater bodies this model was based on the radiative transfer theory which is solved by the doubling matrix method this numerical method provides an explanation for scattering effects due to volume boundaries boundary volume interactions and interactions between layers three ice types were analyzed columnar ice frazil ice and snow ice simulations with the model proved that the radar response from river ice cover depends on both ice cover boundaries the shape and distribution of air inclusions within the different ice types seem to have a significant impact on their contributions to the total response the presence of tubular air inclusions within columnar ice causes an increase in the total response as a result of a double bounce scattering small spherical and closed air inclusions within snow ice and frazil ice generate significant backscattering at high frequencies due to volume and surface volume scattering a further increase in the ice cover thickness with air inclusions also causes increased scattering superposing two or more of these ice types causes considerable multiple scattering between layers finally radar ice measurements collected over the athabasca river were employed to further validate the model and satisfactory results were obtained

puff a high resolution volcanic ash tracking model this paper presents a volcanic ash tracking model referred to as puff the model was developed to simulate the movement of airborne ash in near real time following an eruption for the purposes of hazard warning the model tracks particles through a lagrangian formulation of advection fallout and turbulent diffusion using a random walk technique three recent eruption events are simulated using archived data avhrr images from these events are used for comparison and to validate model results

reflection profiling of arctic lake ice using microwave fm cw radar x and c band fm cw radar reflection profiles were obtained across frozen lakes in northern alaska using a single elevated high gain antenna clear returns were obtained from the air snow snow ice ice water and ice ground interfaces surface to bottom signal intensity ratios are within ranges predicted by plane wave reflection theory use of which also gives plausible permittivity values for the ice rich bottom silts scattering losses are interpreted for the x band ice bottom signals but evidence of increased volumetric scattering loss with increasing ice thickness may have been masked by changes in bottom dielectric contrasts the results suggest that this type of radar is superior to conventional transient gpr systems for this application and ice grounded to almost any type of bottom sediments could be profiled from an airborne platform such a system could help inventory wetland water volume in northern regions

volcanic ash cloud retrieval by ground based microwave weather radar the potential of ground based microwave weather radar systems for volcanic ash cloud detection and quantitative retrieval is evaluated the relationship between radar reflectivity factor ash concentration and fall rate is statistically derived for various eruption regimes and ash sizes by applying a radar reflectivity microphysical model to quantitatively evaluate the ash detectability by weather radars a sensitivity analysis is carried out by simulating synthetic ash clouds and varying ash concentration and size as a function of the range radar specifications are taken from typical radar systems at s c and x band a prototype algorithm for volcanic ash radar retrieval varr is discussed starting from measured single polarization reflectivity the statistical inversion technique to retrieve ash concentration and fall rate is based on two cascade steps namely 1 classification of eruption regime and volcanic ash category and 2 estimation of ash concentration and fall rate expected accuracy of the varr algorithm estimates is evaluated using a synthetic data set an application of the varr technique is finally shown taking into consideration the eruption of the grinodotacutemsvoumltn volcano in iceland on november 2004 volume scan data from a doppler c band radar which is located at 260 km from the volcano vent are processed by means of the varr algorithm examples of the achievable varr products are presented and discussed

erratum to metamictisation of natural zircon accumulation versus thermal annealing of radioactivity induced damage annealing of the radiation damage generated in decay events is a common phenomenon in natural zircons we have studied relationships between radiation damage age and radionuclide content of natural zircons on a micro scale the degree of metamictisation was estimated by means of confocal laser raman spectroscopic measurements raman band broadening in well ordered to moderately metamict zircons that have not experienced significant healing of the radiation damage since the time of their growth shows a nearly linear dependence on the fluence this dependence is proposed as a calibration line for examining unknown zircons in order to consider complete or incomplete damage storage which may contribute to the understanding of the low t thermal history of their host rocks seven examples for the application are presented radiation damage may anneal heterogeneously with preferred re ordering in more damaged micro areas results suggest that single point defects do not anneal continuously over geologic periods of time but are in contrast a comparably stable type of radiation damage in contrast to recrystallisation processes structural recovery due to simple thermal annealing is not necessarily connected with loss of radiogenic pb the most prominent example for this are concordant zircons from sri lanka although they are excellent standards for u pb dating sri lankan zircons should not be used as standards for structural radiation damage the experimental work is completed by monte carlo simulations of decay events in zircon

goes weather satellite observations and measurements of the may 18 1980 mount st helens eruption we demonstrate the use of geostationary operational environmental satellite goes images of the may 18 1980 mount st helens volcanic plume in providing details of the dynamics and changing character of this major explosive eruption visible and thermal infrared ir data from a sequence of images at 30 min intervals from 0850 to 1720 local time lt give information on dispersal and plume top temperature initial visible and ir images at 0850 show the top of a spreading co ignimbrite like umbrella plume and an overshooting column emerging from it both rising off the ground hugging pyroclastic gravity flow generated by the opening directed blast the overshooting column had a minimum temperature significantly colder than local ambient atmosphere indicating substantial undercooling and a maximum altitude of 31 2 km at 0920 this large plume system then formed a high velocity radially spreading gravitationally driven current before becoming advected in the wind field at an average downwind velocity of 29 m s within 30 to 60 min the undercooled plume adjusted to ambient temperatures after this initial event the eruption column fluctuated over the next 8 hours between stable plinian column rise and unstable conditions favoring column collapse leading to pyroclastic flows and further development of co ignimbrite ash columns over this period of observation profiles of plume top temperatures derived from ir data versus distance along the downwind axis have distinctive patterns with steep slopes associated with co ignimbrite plumes and shallower slopes associated with plinian plumes moreover reflectance values from visible goes data change from lower to higher during periods of transition from darker toned plinian to lighter toned coignimbrite plumes indicating that in this case satellite data resolved changes in eruptive style from plumes with a coarser to a finer dominant particle size

dating the cooling of exhumed central uplifts of impact structures by the u th he method a case study at manicouagan abstract forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the manicouagan impact structure were dated by the u th he technique a u th he central age of 207 1 6 4 ma 2 standard error se n 40 has been determined with 4 outlier ages removed the central age is refined to 208 9 5 1 ma 2 se both of these ages are within error of the previously determined u pb zircon age of 214 1 ma 2 derived from the impact melt manicouagan s central uplift formed due to rapid elevation from 7 10 km depth as part of the modification stage of the impact process which has facilitated the dating of its emplacement due to resulting rapid exhumation and cooling and closure of the u th he system in titanite correlation with the previous u pb zircon 214 1 ma impact melt crystallization age indicates that the u th he titanite dating technique offers a new approach to dating complex impact structures in the absence of viable melt sheets or other melt products the youngest ca 195 ma u th he dates preserved in some titanite fragments are synchronous with early jurassic rift induced lithospheric thinning and associated igneous activity that defines the central atlantic magmatic province camp the u th he titanite data from manicouagan indicate that the influence of this regional event may extend west of the previously proposed limit of camp activity

remote observations of eruptive clouds and surface thermal activity during the 2009 eruption of redoubt volcano abstract volcanoes often erupt explosively and generate a variety of hazards including volcanic ash clouds and gaseous plumes these clouds and plumes are a significant hazard to the aviation industry and the ground features can be a major hazard to local communities here we provide a chronology of the 2009 redoubt volcano eruption using frequent low spatial resolution thermal infrared tir mid infrared mir and ultraviolet uv satellite remote sensing data the first explosion of the 2009 eruption of redoubt volcano occurred on march 15 2009 utc and was followed by a series of magmatic explosive events starting on march 23 utc from march 23 april 4 2009 satellites imaged at least 19 separate explosive events that sent ash clouds up to 18 km above sea level asl that dispersed ash across the cook inlet region in this manuscript we provide an overview of the ash clouds and plumes from the 19 explosive events detailing their cloud top heights and discussing the variations in infrared absorption signals we show that the timing of the tir data relative to the event end time was critical for inferring the tir derived height and true cloud top height the ash clouds were high in water content likely in the form of ice which masked the negative tir brightness temperature difference btd signal typically used for volcanic ash detection the analysis shown here illustrates the utility of remote sensing data during volcanic crises to measure critical real time parameters such as cloud top heights changes in ground based thermal activity and plume cloud location

zircon reaction and stability of the u pb isotope system during interaction with carbonate fluid experimental hydrothermal study the interpretation of metamorphically induced u pb isotopic discordance requires a thorough understanding of zircon fluid interactions with this aim we have studied the behaviour of metamict and crystalline zircon phases and their u pb systems by cathodoluminescence after treatment by 2m na2co3 solution at t 200 800 c and p 1 5 kbar for 3 14 days x ray diffraction microprobe and isotope dilution analysis the data indicate that zircon transformation under hydrothermal conditions depends on the experimental conditions and the degree of structural damage reconstitution of defective and impurity enriched zones of metamict zircon homogenization of impure element concentrations and increase of crystallinity was observed at 400 c and p 1 kbar considerable lead and uranium loss occurred under these conditions as a result of zircon dissolution newly formed baddeleyite accommodating u from 2m na2co3 solution and zr na silicate were recognized this process intensified with increasing pressure study of crystalline zircon indicates that migration of u and pb took place only during dissolution of zircon at t above 650 c in the presence of carbonate ions essential u and pb amounts are lost from metamict zircon at a lower p t than is typical for greenschist facies metamorphism

spatial variability of barrow area shore fast sea ice and its relationships to passive microwave emissivity aircraft acquired passive microwave data laser radar height observations radarsat synthetic aperture radar imagery and in situ measurements obtained during the amsr ice03 experiment are used to investigate relationships between microwave emission and ice characteristics over several space scales the data fusion allows delineation of the shore fast ice and pack ice in the barrow area ak into several ice classes results show good agreement between observed and polarimetric scanning radiometer psr derived snow depths over relatively smooth ice with larger differences over ridged and rubbled ice the psr results are consistent with the effects on snow depth of the spatial distribution and nature of ice roughness ridging and other factors such as ice age apparent relationships exist between ice roughness and the degree of depolarization of emission at 10 19 and 37 ghz this depolarization would yield overestimates of total ice concentration using polarization based algorithms with indications of this seen when the nt 2 algorithm is applied to the psr data other characteristics of the microwave data such as effects of grounding of sea ice and large contrast between sea ice and adjacent land are also apparent in the psr data overall the results further demonstrate the importance of macroscale ice roughness conditions such as ridging and rubbling on snow depth and microwave emissivity

rare earth elements in synthetic zircon part 1 synthesis and rare earth element and phosphorus doping zircon crystals were grown from a li mo flux 7 5 mol li2moo4 86 5 mol moo3 to which equal molar proportions zro2 and li2sio3 were added 3 mol each the crystals were initially grown undoped but later dy was added to the flux without any other charge compensating species with dy and p added in equal molar proportions the zircon crystals incorporated 1 37 mol 6 99 wt dy and 1 36 mol 1 33 wt p a factor of 5 3 increase in dy over the crystals grown without p intentionally added to the flux the other p ree doped zircon crystals displayed an approximately 1000 fold increase in ree and p from la through lu a result of decreasing ionic radii the incorporation of p5 allowed in a general sense the xenotime type coupled substitution of ree3 y3 p5 zr4 si4 from la to nd however p exceeds ree from sm to gd the ree are generally equal to p and from tb to lu the ree exceed p the y and p doped zircon behaved more like middle ree mree doped zircon than heavy ree hree doped zircon crystals in their ability to incorporate y and p and to maintain charge neutrality to investigate the incorporation of dy with no p added to the flux the p to lree excess and the hree to p excess in the doped zircon secondary ion mass spectrometry sims analyses were completed on selected crystals in the dy doped crystals the sims analyses revealed minor amounts of p li and mo in the crystals these elements contributed to charge balance required by the excess dy in ree and p doped zircon the sims analyses detected li and mo and the li and mo may also provide charge balance for excess ree in the hree p doped crystals

annealing radiation damage and the recovery of cathodoluminescence the structural recovery upon heat treatment of a highly metamict actinide rich zircon u 6000 ppm has been studied in detail using a range of techniques including x ray powder diffraction raman spectroscopy shrimp ion probe electron microprobe transmission electron microscopy and cathodoluminescence analysis the structural regeneration of the amorphous starting material depends on random nucleation it starts between 800 and 950 c when amorphous zrsio4 decomposes to form crystalline zro2 and amorphous sio2 at around 1100 c well crystallised zrsio4 grows at the expense of the oxides u has been retained in the newly grown zircon whereas pb was evaporated during the heat treatment this process is in marked opposition to the reconstitution of moderately metamict minerals which experience a gradual recovery controlled by the epitaxial growth at the crystalline amorphous boundaries both of these recovery processes are not the direct inverse of metamictisation the structural regeneration was found to be connected with a significant increase in the emission of cl in all cases annealing heavily damaged zircon and moderately damaged zircon and monazite we observe that the final wellcrystallised annealing products emit more intense cl than their radiation damaged starting minerals although having almost identical elemental composition our observations are taken as evidence that the cl is not only determined by the chemical composition of the sample but is also strongly controlled by structural parameters such as crystallinity or the presence of defect centres

misr observations of etna volcanic plumes 1 in the last twelve years mt etna located in eastern sicily has produced a great number of explosive eruptions volcanic plumes have risen to several km above sea level and created problems for aviation and the communities living near the volcano a reduction of hazards may be accomplished using remote sensing techniques to evaluate important features of volcanic plumes since 2000 the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft has been extensively used to study aerosol dispersal and to extract the three dimensional structure of plumes coming from anthropogenic or natural sources including volcanoes in the present work misr data from several explosive events occurring at etna are analyzed using a program named minx misr interactive explorer minx uses stereo matching techniques to evaluate the height of the volcanic aerosol with a precision of a few hundred meters and extracts aerosol properties from the misr standard products we analyzed twenty volcanic plumes produced during the 2000 2001 2002 03 2006 and 2008 etna eruptions finding that volcanic aerosol dispersal and column height obtained by this analysis is in good agreement with ground based observations misr aerosol type retrievals 1 clearly distinguish volcanic plumes that are sulphate and or water vapor dominated from ash dominated ones 2 detect even low concentrations of volcanic ash in the atmosphere 3 demonstrate that sulphate and or water vapor dominated plumes consist of smaller sized particles compared to ash plumes this work highlights the potential of misr to detect important volcanic plume characteristics that can be used to constrain the eruption source parameters in volcanic ash dispersion models further the possibility of discriminating sulphate and or water vapor dominated plumes from ash dominated ones is important to better understand the atmospheric impact of these plumes

helium irradiation study on zircon synthetic zrsio4 and mildly to strongly radiation damaged natural zircon samples were irradiated with 8 8 mev 4he2 ions fluences in the range 1 1013 5 1016 ions cm2 for comparison an additional irradiation experiment was done with 30 mev 16o6 ions fluence 1 1015 ions cm2 the light ion irradiation resulted in the generation of new synthetic zrsio4 or additional mildly to strongly metamict natural samples damage the maximum extent of the damage is observed in a shallow depth range approximately 32 33 m 8 8 mev he and 12 m 30 mev o below the sample surface i e near the end of the ion trajectories these depth values and the observed damage distribution correspond well to defect distribution patterns as predicted by monte carlo simulations the irradiation damage is recognised from the notable broadening of raman active vibrational modes lowered interference colours i e decreased birefringence and changes in the optical activity i e luminescence emission at very low damage levels a broad band yellow emission centre is generated whereas at elevated damage levels this centre is suppressed and samples experience a general decrease in their emission intensity most remarkably there is no indication of notable structural recovery in pre damaged natural zircon as induced by the light ion irradiation which questions the relevance of alpha assisted annealing of radiation damage in natural zircon

qualitative comparison of mount redoubt 2009 volcanic clouds using the puff and wrf chem dispersion models and satellite remote sensing data abstract satellite remote sensing data presents an important tool to map and analyze airborne volcanic ash both spatially and temporally however such data only represents an instant in time to supplement the satellite data and to forecast plume and cloud movement volcanic ash transport and dispersion models are used mount redoubt volcano erupted in march and april 2009 with 19 detected events by analyzing events 5 and 19 we show how satellite data can be used in combination with puff and the weather research and forecast model with online chemistry wrf chem wrf chem has been combined and initialized with a volcanic eruption model puff as well as wrf chem show a good assessment of the plume characteristics compared to the satellite data especially for event 19 we observed a very close match between wrf chem and satellite data where puff showed an offset of the predicted plume

a multi sensor plume height analysis of the 2009 redoubt eruption abstract during an explosive volcanic eruption accurately determining the height of a volcanic plume or cloud is essential to accurately forecast its motion because volcanic ash transport and dispersion models require the initial plume height as an input parameter the direct use of satellite infrared temperatures for height determination one of the most commonly employed methods at the alaska volcano observatory often does not yield unique solutions for height this result is documented here for the 2009 eruption of redoubt volcano satellite temperature heights consistently underestimated the height of ash plumes in comparison to other methods such as ground based radar and multi angle imaging spectroradiometer misr stereo heights for ash plumes below the tropopause increasing transparency of a plume begins to affect the accuracy of simple temperature height retrievals soon after eruption with decreasing opacity plume temperature heights become increasingly inaccurate comparison with dispersion models and aircraft gas flight data confirms that radar and misr stereo heights are more accurate than basic satellite temperature heights even in the cases in which satellite temperature results appeared to be relatively accurate e g for plumes below the tropopause a mixed signal of plume and ground radiation still presented an issue for almost every event studied this was true regardless of the fact that a band differencing method was used to remove presumably translucent pixels the data presented here make a strong case for the use of data fusion in volcano monitoring as there is a need to confirm satellite temperature heights with other height data if only basic satellite temperature heights are available for a given eruption then these heights must be considered with a significant margin of error

predicting regions susceptible to high concentrations of airborne volcanic ash in the north pacific region abstract airborne ash probability distribution aapd maps have been generated to show the distribution of airborne volcanic ash in the north pacific nopac region by simulating volcanic eruption clouds from 22 of the 100 most historically active volcanoes in the region the puff ash dispersion model was run daily using archived wind field data between 1994 1995 and 1997 2001 for low and high aircraft flight levels subsequent statistics are generated representing the distribution of simulated airborne ash at 6 and 24 h intervals defining the regions most likely to contain airborne ash and the direction and distance a volcanic ash cloud may propagate from a given volcano the aapd maps show the extent of ash from a given volcano can encompass all of alaska most of the north pacific ocean portions of northwestern north america regions as far south as 35 n regions over the western arctic ocean and portions of eastern russia in general low altitude atmospheric regions 3 8 km asl are more susceptible to airborne volcanic ash when compared to regions above 8 km asl due to the eruption characteristics of volcanoes in the north pacific and the region s atmospheric profile the results indicate that the paths of many nopac air traffic routes coincide with airborne ash distribution probability maxima the upper atmospheric region most likely to contain airborne ash is located off the eastern coast of the kamchatkan peninsula and is generally centered over the heavy air traffic flight corridor of the nopac although this paper focuses on the nopac region the technique can be directly applied to other regions characterized by active volcanism

extending the time range of apatite u th he thermochronometry in slowly cooled terranes palaeozoic to cenozoic exhumation history of southeast sweden the use of u th he thermochronometry in old slowly cooled terranes has long been debated hence studies of natural setting are needed to verify the expected diffusivity behaviour of helium our results demonstrate that the u th he method can be applicable to samples older than 200 ma and that available helium diffusion models can reproduce the results obtained from the age vs depth trends in addition the results shed some light on the cross validation with the apatite fission track thermochronometer u th he thermochronometry on apatites has been applied to samples taken from drill cores in the precambrian basement in southeast sweden to unravel the time of exhumation of the uppermost 1 3 km of the crust much of the phanerozoic exhumation history in sweden is poorly constrained due to a large hiatus in the sediment record results from the drill cores yield he ages decreasing with increasing depth from similar to 270 ma at the surface down to similar to 120 ma at 1700 in depth the age vs depth trend shows an inflection point at similar to 1400 in depth which coincides with the upper boundary of the present helium partial retention zone a period of slow exhumation similar to 17 m my probably linked to the isostatic uplift of the caledonian foreland basin is revealed by the upper section of the trend in the data the results demonstrate that the area has not been reheated since the mid permian this argues against the existence of a thick mesozoic sedimentary cover in this region which if present at all cannot have exceeded 100 in in thickness furthermore the age vs depth trend below the inflection point allows dating the cessation of exhumation at approximately 100 ma the area has had no significant amount of sedimentation erosion or uplift since this time less

metamictization and chemical durability of detrital zircon we have investigated the effect that metamictization has on the weathering of zircon in detrital continental sediments and tropical soils of the amazon basin brazil the degree of radiation damage in the near surface region of the zircon grains was determined by raman microprobe in each of the four series investigated i e sediment podzol topsoil and subsoil horizons of lateritic soil the degree of radiation damage ranges from less than 1014 to 3 5 1015 decay mg the maximum degree of radiation damage coincides with the first percolation threshold of the metamictization process at 3 5 1015 decay mg below this threshold amorphous volumes in the structure of damaged zircon are not connected to each other the ranges of u th and pb contents in ppm measured by proton induced x ray emission pixe microanalysis are 100 u 7000 100 th 18000 and 100 pb 1300 chemical ages assessed from u th and total pb range between 0 15 ga and 2 8 ga this range is roughly consistent with the ages reported for the precambrian shields of the amazon basin 0 45 3 5 ga corresponding radiation doses range between 2 1015 and 3 1016 decay mg comparison of calculated doses with the degree of structural damage indicates that most of the zircon grains have experienced significant annealing however the degree of annealing differs from one grain to another thus the acute maximum limit observed for the degree of radiation damage of the whole zircon series is better explained by low temperature alteration or weathering processes than by thermal resetting following this interpretation our results provide evidence for a dramatic decrease in the chemical durability of zircon in natural weathering environments when the radiation dose exceeds 3 5 1015 decay mg below the first percolation threshold the zircon population survives the soil formation intact but more damaged zircons are dissolved during weathering alteration processes

helium diffusion in rutile and titanite and consideration of the origin and implications of diffusional anisotropy abstract diffusion of helium has been characterized in natural sphene titanite and synthetic rutile polished slabs of sphene and rutile were implanted with 100 kev 3he at a dose of 5 1015 3he cm2 and annealed in 1 atm furnaces 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in rutile we obtain the following arrhenius relations d a 2 26 1 0 1 0 exp 126 11 kj mol 1 rt m 2 sec 1 d c 1 75 1 0 8 exp 12 0 7 kj mol 1 rt m 2 sec 1 although activation energies for diffusion parallel to the c and a axes are comparable there is marked diffusional anisotropy with diffusion parallel to the c axis about 2 orders of magnitude faster than transport parallel to the a axis these diffusivities bracket the values determined for he diffusion in rutile in bulk release experiments stockli et al 2005 stockli et al 2007 wolfe 2009 although the role of anisotropy could not be directly evaluated in those measurements in titanite the following arrhenius relation was obtained over the temperature range 252 550 c for diffusion parallel to the a axis d 2 14 1 0 6 exp 148 8 kj mol 1 rt m 2 sec 1 in contrast to rutile and zircon cherniak et al 2009 titanite shows little evidence of anisotropy as diffusivities parallel to the a and c axes are similar and diffusivities for titanites from two different localities are similar he diffusion coefficients obtained in this study are similar to those measured through bulk release of he by step heating shuster et al 2003 over the investigated temperature range diffusion of he in titanite is similar to that of he diffusion in rutile parallel to the c axis but much faster than diffusion parallel to the a axis since the diffusion of he in rutile exhibits such pronounced anisotropy we model diffusional loss of he with a recently developed finite element code watson et al 2010 created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients we present example applications to evaluate helium losses from rutile grains as a function of grain size and length to diameter ratios in efforts to better understand the occurrence of pronounced anisotropy for he diffusion in some crystals e g rutile zircon but not in others e g apatite titanite we consider the density and distribution of interstitial apertures in the crystal structure that might permit he migration these determinations an extension of the concept of ionic porosity are consistent with observations of relative diffusivities and the existence or absence of significant anisotropy for the minerals rutile zircon apatite and titanite

radar backscattering of lake ice during freezing and thawing stages estimated by ground based scatterometer experiment and inversion from genetic algorithm lake ice under phase transition shows large variation on radar backscattering due to the changes of dielectric constant and roughness of ice surface and thus the transmissivity of microwave into ice body to study the effects of freezing thawing of ice on radar backscattering in a short time we spread water over lake ice and continuously measured radar backscattering by using a ground based microwave scatterometer system operated in c band hh polarization by establishing scattering models and applying inversion from genetic algorithm radar returns were separated into ice surface volume and ice bottom scatterings and the changes in dielectric constant and roughness parameters of ice surface were estimated as well immediately after spreading water on ice surface ice surface scattering was strongest due to high dielectric constant of surface water while volume and ice bottom scatterings were very weak due to low microwave transmissivity into ice body as surface water was being frozen ice surface scattering became weak with decreasing dielectric constant while volume and ice bottom scattering increased due to higher transmissivity into ice body in a transition stage when surface water was almost frozen all three scatterings increased simultaneously crystallization of ice produced rougher surface overcoming the decrease in dielectric constant resulting in the increase of ice surface scattering while volume and ice bottom scattering was continuously increased due to increasing transmissivity at the end of the experiment air temperature rose above freezing point and ice surface thawed again so that ice surface scattering increased while volume and ice bottom scattering were decreased

doppler weather radar observations of the 2009 eruption of redoubt volcano alaska abstract the u s geological survey usgs deployed a transportable doppler c band radar during the precursory stage of the 2009 eruption of redoubt volcano alaska that provided valuable information during subsequent explosive events we describe the capabilities of this new monitoring tool and present data captured during the redoubt eruption the minimax 250 c mm 250c radar detected seventeen of the nineteen largest explosive events between march 23 and april 4 2009 sixteen of these events reached the stratosphere above 10 km within 2 5 min of explosion onset high column and proximal cloud reflectivity values 50 to 60 dbz were observed from many of these events and were likely due to the formation of mm sized accretionary tephra ice pellets reflectivity data suggest that these pellets formed within the first few minutes of explosion onset rapid sedimentation of the mm sized pellets was observed as a decrease in maximum detection cloud height the volcanic cloud from the april 4 explosive event showed lower reflectivity values due to finer particle sizes related to dome collapse and related pyroclastic flows and lack of significant pellet formation eruption durations determined by the radar were within a factor of two compared to seismic and pressure sensor derived estimates and were not well correlated ash dispersion observed by the radar was primarily in the upper troposphere below 10 km but satellite observations indicate the presence of volcanogenic clouds in the stratosphere this study suggests that radar is a valuable complement to traditional seismic and satellite monitoring of explosive eruptions

apatite fission track and u th he data from fennoscandia an example of underestimation of fission track annealing in apatite abstract apatite fission track aft data from cratons have commonly been interpreted in terms of major episodes of sedimentary burial and subsequent denudation often in the absence of any remnant sedimentary rocks or other supporting geological evidence reconciling these interpretations with geologically documented denudation events or outcropping regional stratigraphy can be problematic also u th he ages from cratonic igneous rocks that are older than paired aft data are commonly discarded as too old even when the former are repeatable at the 2 confidence level for example aft data from central fennoscandia have been interpreted to reflect first burial by a caledonian foreland basin several kilometres in thickness and subsequently its denudation however throughout fennoscandia there is no direct evidence that such a deep extensive foreland basin ever existed and indeed some geological evidence points to the contrary additionally a significant number of u th he ages from fennoscandia are older than their aft pairs but have been interpreted by their authors as too old relative to the aft ages and not geologically meaningful despite repeatable results here we propose a new interpretation of aft data from fennoscandia that closely reflects the observed data yet is compatible with the generally accepted geological history discarding the hypothesis of a thick caledonian foreland basin we suggest that 1 aft ages in finland are too young rather than that the u th he ages are too old 2 repeatable sequences of u th he ages are more likely to record the true denudation history of cratons 3 the importance of radiation enhanced annealing at low temperatures has been overlooked and 4 fennoscandian aft data may be divided into an eastern domain strongly affected by radiation enhanced annealing where current aft annealing models are invalid and a western domain much less affected by radiation enhanced annealing where current modelling methods may appropriately be used to extract thermal histories in principle radiation enhanced annealing is also pertinent to the interpretation of young aft ages from apatites rich in emitter actinides the construction of a properly calibrated annealing model that fully incorporates the effects of radiation enhanced annealing is fundamentally important

limits to future expansion of surface melt enhanced ice flow into the interior of western greenland moulins are important conduits for surface meltwater to reach the bed of the greenland ice sheet it has been proposed that in a warming climate newly formed moulins associated with the inland migration of supraglacial lakes could introduce surface melt to new regions of the bed introducing or enhancing sliding there by examining surface strain rates we found that the upper limit to where crevasses and therefore moulins are likely to form is 1600m this is also roughly the elevation above which lakes do not drain completely thus meltwater above this elevation will largely flow tens of kilometers through surface streams into existing moulins downstream furthermore results from a thermal ice sheet model indicate that the 1600m crevassing limit is well below the wet frozen basal transition 2000m together these data sets suggest that new supraglacial lakes will have a limited effect on the inland expansion of melt induced seasonal acceleration key points greenland ice sheet meltwater volumes are increasing notably at high elevations low strain rates limit the likelihood of moulin formation at high elevations high elevation meltwater will reach an already wet bed at lower elevations

improved accuracy of zircon u th he ages by rectifying parent nuclide zonation with practical methods abstract a major limitation in the accuracy of zircon u th he thermochronometry zhe is the alpha ejection correction the standard alpha ejection correction f t assumes a homogeneous u th distribution in the host crystal here two approaches are used to address parent nuclide heterogeneity often observed in natural zircons 1 a new methodology where offending zonation is mechanically removed and 2 custom alpha ejection corrections informed by a la icp ms depth profile f zac we present an empirical test of these methodologies on a suite of bedrock zircons from variscan orthogneisses of the central aegean which display marked parent nuclide zonation which has impacted the ability to obtain accurate and precise thermochronometric data during the progressive mechanical abrasion of enriched u th and he zones the change in grain diameter exhibits a parabolic relationship with respect to the apparent age where the youngest age should represent the true age of the sample the abrasion corrected weighted mean age for sample 08pa01 is 8 8 0 7 ma f t 1 a too young age possibly the result of parent nuclide enriched cores the findings also show that using f zac instead of f t may change single sample zhe aliquots up to 29 using f zac increases the weighted mean age 17 for sample 08pa01 from 9 2 0 7 ma f t to 10 8 0 9 ma f zac and 6 for sample 08pa71 from 10 9 0 8 f t ma to 11 5 0 9 ma f zac in this case the f zac correction improves the overall accuracy of the zhe data but does not impact the problem of over dispersed ages suggesting they may be separate issues the increase in zhe age brings the dataset into agreement with previous thermochronometric studies indicating that cooling of the paros footwall below 180 c may have occurred earlier than hitherto thought

near real time volcanic ash cloud detection experiences from the alaska volcano observatory volcanic eruptions produce ash clouds which are a major hazard to population centers and the aviation community within the north pacific nopac region there have been numerous volcanic ash clouds that have reached aviation routes others have closed airports and traveled for thousands of kilometers being able to detect these ash clouds and then provide an assessment of their potential movement is essential for hazard assessment and mitigation remote sensing satellite data through the reverse absorption or split window method is used to detect these volcanic ash clouds with a negative signal produced from spectrally semi transparent ash clouds single channel satellite is used to detect the early eruption spectrally opaque ash clouds volcanic ash transport and dispersion vatd models are used to provide a forecast of the ash clouds future location the alaska volcano observatory avo remote sensing ash detection system automatically analyzes satellite data of volcanic ash clouds detecting new ash clouds and also providing alerts both email and text to those with avo however there are also non volcanic related features across the nopac region that can produce a negative signal these can complicate alerts and warning of impending ash clouds discussions and examples are shown of these non volcanic features and some analysis is provided on how these features can be discriminated from volcanic ash clouds finally there is discussion on how information of the ash cloud such as location particle size and concentrations could be used as vatd model initialization these model forecasts could then provide an improved assessment of the clouds future movement

reducing discrepancies in ground and satellite observed eruption heights abstract the plume height represents a crucial piece of evidence about an eruption feeding later assessment of its size character and potential impact and feeding real time warnings for aviation and ground based populations there have been many observed discrepancies between different observations of maximum plume height for the same eruption a comparison of maximum daily height estimates of volcanic clouds over indonesia and papua new guinea during 1982 2005 shows marked differences between ground and satellite estimates and a general tendency towards lower height estimates from the ground without improvements in the quality of these estimates reconciled among all available methods warning systems will be less effective than they should be and the world s record of global volcanism will remain hard to quantify examination of particular cases suggests many possible reasons for the discrepancies consideration of the satellite and radar cloud observations for the 1991 pinatubo eruptions shows that marked differences can exist even with apparently good observations the problem can be understood largely as a sampling issue as the most widely reported parameter the maximum cloud height is highly sensitive to the frequency of observation satellite and radar cloud heights also show a pronounced clumping near the height of the tropopause and relative lack of eruptions reaching only the mid troposphere reinforcing the importance of the tropopause in determining the eruption height in convectively unstable environments to reduce the discrepancies between ground and satellite estimates a number of formal collaboration measures between vulcanological meteorological and aviation agencies are suggested

reconstructing hydrographic change in petersen bay ellesmere island canada inferred from sar imagery abstract synthetic aperture radar sar satellite imagery was used to reconstruct the change in limnological conditions adjacent to an arctic ice shelf by examining the backscatter values of coastal ice in mid winter scenes high sar backscatter values 6 db suggest that an ice dammed lake was present adjacent to the south coast of petersen bay from 1992 until 2005 following a large calving event of the adjacent petersen ice shelf 8 07 km2 in august 2005 the lake drained through a region where the ice shelf had separated from the coastline this loss of freshwater and replacement of lake ice with sea ice along the southern coast of petersen bay were confirmed from analyses of ice core samples and conductivity temperature depth ctd profiles the exception to this pattern was one distinct area where terrestrial streams entered the edge of petersen bay and freshwater continued to collect from 2006 to 2008 however this ephemeral area of freshwater has not reformed since 2009 due to the persistence of open water events in petersen bay observed in optical satellite imagery which likely facilitated mixing of freshwater with sea water based on the continued break ups of petersen ice shelf and the frequency of open water events it is unlikely that this ice dammed lake will reform the results of this study underscore the utility of sar for reconstructing past hydrographic conditions in the water column below

assessing the altitude and dispersion of volcanic plumes using misr multi angle imaging from space sixteen years of volcanic activity in the kamchatka peninsula russia abstract volcanic eruptions represent a significant source of atmospheric aerosols and can display local regional and global effects impacting earth systems and human populations in order to assess the relative impacts of these events accurate plume injection altitude measurements are needed in this work volcanic plumes generated from seven kamchatka peninsula volcanoes shiveluch kliuchevskoi bezymianny tolbachik kizimen karymsky and zhupanovsky were identified using over 16 years of multi angle imaging spectroradiometer misr measurements eighty eight volcanic plumes were observed by misr capturing 3 25 of reported events at individual volcanoes retrievals were most successful where eruptive events persisted over a period of weeks to months compared with existing ground and airborne observations and alternative satellite based reports compiled by the global volcanism program gvp misr plume height retrievals show general consistency the comparison reports appear to be skewed towards the region of highest concentration observed in misr constrained plume vertical extent the report observations display less discrepancy with misr toward the end of the analysis period 2013 2016 with improvements in the suborbital data likely the result of the deployment of new instrumentation conversely the general consistency of misr plume heights with conventionally reported observations supports the use of misr in the ongoing assessment of volcanic activity globally especially where ground based observations are unavailable differences between the northern shiveluch kliuchevskoi bezymianny and tolbachik and southern kizimen karymsky and zhupanovsky volcanoes broadly corresponding to the central kamchatka depression ckd and eastern volcanic front evf geological sub regions of kamchatka respectively are distinguished by varying magma composition for example by comparison with reanalysis model simulations of local meteorological conditions ckd plumes were generally less constrained by mid tropospheric

a sar record of early 21st century change in greenland glaciers in greenland are changing rapidly to better understand these changes we have produced a series of seven synthetic aperture radar sar backscatter mosaics for seven winters during the period from 2000 to 2013 six of the mosaics were created using radarsat fine beam data and the seventh used alos palsar fine beam single polarization data the radarsat mosaics are radiometrically calibrated and capture changes in the backscatter coefficient related to melt and other events particularly the strong melting in the summer of 2012 comparison of features in the ascending orbit alos mosaic and the descending orbit radarsat mosaics indicate that in areas of smooth to moderate topography their locations are consistent to within a few 10s of meters the locations of features identifiable in the radarat mosaics which were collected with the same imaging parameters generally agree to within better than the 20 m posting of the data with such geometric accuracy these data establish a record of change in greenland for the early part of the 21st century thus providing a baseline that can be compared with new radar and optical data sets

retrievals of lake ice thickness from great slave lake and great bear lake using cryosat 2 satellite observations have revealed decreases in the duration of the seasonal snow and ice coverage of great slave lake gsl and great bear lake gbl large freshwater lakes in northern canada however limited information is available about ice thickness changes here we present and validate a method to retrieve lake ice thickness using the cryosat 2 cs2 radar altimeter these are the first satellite altimeter retrievals of lake ice thickness under optimal conditions the cs2 signal is scattered from both the snow ice and the ice water interfaces with returns from each interface being of sufficient power to be identified in the radar waveform the distance between the scattering horizons is used to determine the ice thickness similar to traditional ground penetrating radar measurements the seasonal evolution of ice thickness of gbl and gsl is compared with in situ measurements modeled ice thicknesses and previous studies the impact of ice and snow properties on signal penetration and the thickness retrieval are examined with synthetic aperture radar imagery the cs2 ice thickness retrievals are able to observe the seasonal thickening of the lake ice and closely match the in situ measurements over both lakes r 0 65 text rmse m thickness retrievals of thin ice are limited by a minimum waveform peak separation of 2 range bins approximately 0 26 m in ice although not designed for lake ice studies cs2 and future sar satellite altimeter missions offer new possibilities to monitor the ice and water levels of climatically sensitive and influential lakes

failures in detecting volcanic ash from a satellite based technique abstract immediate and accurate detection of airborne volcanic ash is an operational imperative of the aviation industry especially jet aircraft ash encounters place passengers aboard these aircraft at severe risk and significantly impact via forced rerouting both the safety and profit margins of freight carriers due to their limited fuel supply moreover the airlines can suffer high economic costs for repair and replacement of equipment operational detection and tracking of volcanic ash by most national weather services has relied heavily on a split window differencing technique of thermal longwave infrared channels on currently operational satellites unfortunately prior work on volcanic ash detection has not emphasized the dynamical interaction between the erupting volcano and the effects of overlying atmospheric water vapor phreatic and phreatomagmatic water sources six volcanic ash eruptions from around the globe were chosen for study because they have wide variation in ambient atmospheric water vapor available ground and surface water and different magma types results show that the present differencing technique is not uniformly effective in properly classifying volcanic ash pixels in the satellite scene and often falsely interprets meteorological clouds as volcanic ash clouds and conversely moreover it is not always a robust early detector an operational aviation requirement seasonal variability in global integrated atmospheric water vapor coupled with the geographical distribution of currently active volcanoes suggests the concerns discussed herein with regard to six specific eruptions have applicability to the global aviation industry operational implications are discussed and a strategic proposal is presented on necessary steps to improve detection

aufeis in the ivishak river alaska mapped from satellite radar interferometry abstract aufeis deposits form every year on many rivers on the north slope of alaska and through repeated episodes of overflow and freezing they may reach a thickness of more than 3 m the presence of aufeis in a drainage basin tends to stabilize river discharge in the same way as a glacier does by providing melt water during hot dry periods this distribution of aufeis deposits along the rivers is discontinuous because of variations in channel geometry and under ice water supply and monitoring their growth during the winter is generally impractical however experiments using satellite radar interferometry sri to map changes in the extent of aufeis near the junction of the ivishak and the echooka rivers in the northern brooks range during the winter have produced promising results interferograms of the area were made from pairs of images acquired by the european space agency s first earth remote sensing satellite in january through march 1994 the results indicate that aufeis deposits can be mapped on interferograms as areas in river valleys in which the radar phases are poorly correlated and radar backscatter values frequently change the ability of sri in monitoring subtle winter aufeis processes fills a major gap in the study of aufeis by remote sensing

analysis of ers 1 synthetic aperture radar data of frozen lakes in northern montana and implications for climate studies lakes that freeze each winter are good indicators of regional climate change if key parameters such as freeze up and breakup date and maximum ice thickness are measured over a decade scale time frame synthetic aperture radar sar satellite data have proven to be especially useful for measurement of climatologically significant parameters characteristic of frozen lakes in this paper five lakes in glacier national park montana have been studied both in the field and using ers 1 sar data during the 1992 1993 winter the lakes are characterized by clear ice sometimes with tubular or rounded bubbles and often with a layer of snow ice on top of the clear ice they are also often snow covered freeze up is detected quite easily using ers 1 sar data as soon as a thin layer of ice forms the effect of snow ice on the backscatter is thought to be significant but is as yet undetermined on the five lakes studied relative backscatter was found to increase with ice thickness until a maximum was reached in february breakup an often ill defined occurrence is difficult to detect because surface water causes the sar signal to be absorbed thus masking the ice below comparison of the bubble structure of thaw lakes in northern alaska with lakes in northern montana has shown that the ice structure is quite different and this difference may contribute to differential sar signature evolution in the lakes of the two areas

observing lake and river ice decay with sar advantages and limitations of the unsupervised k means classification approach large parts of the arctic are covered by water bodies ice covers on lakes and rivers prohibit the exchange of heat and water vapor between the water body and the atmosphere with melt onset the ecosystem is subjected to changes making it important to monitor the ice decay as ground based monitoring of these vast uninhabited areas is expensive and thus restricted to a few locations remote sensing techniques need to be applied here we evaluate the performance of the unsupervised k means classification for dividing ice and water fractions on lakes and river channels from spaceborne radar data in comparison to threshold based methods the analysis is based on six terrasar x and three radarsat 2 images obtained during spring 2011 over the central lena delta in northern siberia the performance of the k means classification is found to be similar to a fixed threshold approach as the k means classification does not need prior statistical backscatter analyses to account for the radar configuration and ice conditions it is easier to use than the threshold method in addition we found that the application of a low pass filter prior to the classification of river channels and a closing filter on the classification results of lakes strongly improves the overall classification results

incomplete retention of radiation damage in zircon from sri lanka a suite of 18 zircon gemstones from placers in the highland southwestern complex sri lanka were subjected to a comprehensive study of their radiation damages and ages the investigation included x ray diffraction raman and pl spectroscopy electron microprobe pixe and hrtem analysis as well as u th he and shrimp u th pb age determinations zircon samples described in this study are virtually homogeneous they cover the range from slightly metamict to nearly amorphous generally concordant u th pb ages averaging 555 11 ma were obtained late ordovician zircon u th he ages scattering around 443 9 ma correspond reasonably well with previously determined biotite rb sr ages for rocks from the hswc slightly to moderately metamict zircon has retained the radiogenic he whereas only strongly radiation damaged zircon calculated total fluences exceeding 3 5 10 18 events g has experienced significant he loss when compared to unannealed zircon from other localities sri lanka zircon is about half as metamict as would correspond to complete damage accumulation over a 555 m y lasting self irradiation period suggesting significant annealing of the structural radiation damage insufficient consideration of this has often resulted in significant underestimation of radiation effects in zircon we suggest to estimate effective doses for sri lanka zircon by multiplying total fluences which were calculated using the zircon u th pb age by a correction factor of 0 55 this conversion may be applied to literature data as well because all gem zircon samples from sri lanka this work and previous studies seem to reveal the same general trends of property changes depending on the radiation damage the use of effective doses for sri lanka zircon contributes to more reliable quantitative estimates of radiation effects and makes possible direct comparison between natural and synthetic radiation damaged zircon