changes in tourmaline composition during magmatic and hydrothermal processes leading to tin ore deposition the cornubian batholith sw england abstract to investigate the potential of tourmaline as a geochemical monitor a comprehensive dataset on major minor and trace element concentrations as well as fe3 fe ratios of tourmaline is presented the dataset includes samples from five plutonic complexes related to diverse magmatic to hydrothermal stages of the cornubian batholith sw england tourmaline composition found in barren and cassiterite bearing samples include all three primary tourmaline groups and tourmaline species with the general endmembers schorl dravite elbaite uvite feruvite foitite and mg foitite based on textures and compositions it is possible to distinguish not only between late magmatic and hydrothermal tourmaline but also between several formation stages hence tourmaline monitors late magmatic processes and the partitioning of elements during exsolution of an aqueous phase for example in hydrothermal tourmaline sn is strongly enriched while ti cr v and sc are depleted compared to late magmatic tourmaline of the same sample several tourmaline generations that precipitated from magmatic fluids can be distinguished with differing major and minor elements and ree patterns depending on the composition of the melt from which they were expelled from strongly zoned tourmaline allows for unraveling the hydrothermal history of a distinct location including ore precipitation the precipitation of sno2 in the study area was probably caused by mixing between acidic reduced sn bearing magmatic fluids and oxidized meteoric fluids which is in agreement with london and manning 1995 and williamson et al 2000 hence the ability of tourmaline composition to monitor changes in sn concentration and redox conditions in hydrothermal fluids has potential as an exploration tool

deducing the thermal structure in the tongue of gornergletscher switzerland from radar surveys and borehole measurements we present the thermal distribution in the confluence area of gorner and grenzgletscher valais switzerland the area was mapped by ice penetrating radar at 1 5 and 40 mhz the higher frequency data reveal a thick surface layer of low backscatter in the center of the grenzgletscher branch based on datasets of borehole temperature measurements and flow velocity we interpret this as a thick layer of cold ice advected from the accumulation region of grenzgletscher along seven profiles the base of the low backscatter zone can be found at a maximum depths between approxi mately 100 and 200 m laterally the layer extends some 400 m 1 3 of the width of the grenz gletscher branch the lower boundary of the low backscatter zone is systematically higher than the cold temperate transition surface found in the boreholes this discrepancy is attributed to the direct sensitivity of radar backscatter to liquid water inclusions rather than to the temperature distributions as observed in boreholes we present the current state of the cold layer and discuss its influence on other glacier characteristics

cold surface layer thinning on storglaciaren sweden observed by repeated ground penetrating radar surveys 1 a characteristic feature of ground penetrating radar gpr surveys on polythermal glaciers is an internal reflection presumably caused by the cold temperate transition surface cts hence providing a possible tool for mapping thermal structure with high accuracy comparison of detailed temperature measurements in bore holes and gpr profiles at 345 mhz and 800 mhz center frequencies on storglaciaren sweden show that the cts can be detected and mapped with an accuracy of about 1 m at both frequencies a comparison between comprehensive gpr surveys of the cold surface layer separated by 12 years 1989 2001 shows a substantial and complex thinning of the cold layer an overall decrease of 8 3 m 22 of average thickness of the cts depth is much larger than uncertainties in cts depth determinations the stability of the cold surface layer depends on the net ice ablation at the surface and the downward migration of cts there is no evidence of substantial increased net ablation between the survey dates that could explain the observed thinning however small increase in average winter air temperature a limiting factor for the temperature gradient through the cold surface layer may provide a partial explanation the weaker temperature gradient reduces the transport of latent heat from the cts thus slowing down its downward migration

estimating the risk of glacier cavity collapse during artificial drainage the case of tete rousse glacier 1 during the summer of 2010 the presence of a pressurized water filled subglacial cavity of at least 50 000 m3 was detected within the tete rousse glacier french alps artificial drainage was started to avoid an uncontrolled rupture of the ice dam but was interrupted soon after to evaluate the capacity of the cavity roof to bear itself the risk was that the release of pressure within the cavity during the artificial drainage would precipitate the collapse of the cavity roof and potentially flush out the remaining water flooding the valley below an unprecedented modeling effort was deployed to answer the question of the cavity roof stability we set up a model of the glacier with its water cavity solved the three dimensional full stokes problem predicted the upper surface and cavity surface displacements for various drainage scenarios and quantified the risk of the cavity failure during artificial drainage we found that the maximum tensile stress in the cavity roof was below the rupture value indicating a low risk of collapse a post drainage survey of the glacier surface displacements has confirmed the accuracy of the model prediction this practical application demonstrates that ice flow models have reached sufficient maturity to become operational and assist policy makers when faced with glaciological hazards thus opening new perspectives in risk management of glacier hazards in high mountain regions

latitude variations in light scattered from polar mesospheric clouds a middle ultraviolet imager over the northern and southern polar regions has measured the scattered intensities of polar mesospheric clouds pmc during the austral summer of 1997 98 and the arctic summer of 1999 the intensities corrected for solar zenith angle are those at the peak in the pmc radiance profiles for a waveband of 235 263 nm the peak radiance averaged 12 0 11 0 mega rayleighs mr for 13 passes over the south polar region where the scattering angle was 111 the peak radiance averaged 11 4 7 6 mr for 12 passes over the north polar region where the scattering angle was 48 the pmc intensities increased with increasing latitude in both the north and the south but the rate of increase was twice as fast in the south 0 60 mr latitude as in the north 0 32 mr latitude

vertical distribution of water within the polythermal storglaciaren sweden 1 knowledge of water content and its distribution in polythermal glaciers is required to model their flow and thermal state however observations of water content variations with depth in polythermal glaciers are scarce water content can be estimated from radio wave speed because they depend on one another we obtained continuous profiles of radio wave speed variations with depth from zero offset radar profiles collected in boreholes approximately 80 m deep in the upper ablation area of storglaciaren northern sweden these profiles show that the microcrystalline water system in the temperate ice is relatively homogeneous the overall hydrothermal structure at this location is composed of a 20 m thick upper layer of cold water free ice underlain by a temperate ice layer whose average water content is 0 6 0 3 these results are corroborated by surface radar and thermistor measurements which show that the depth of the cold temperate transition is 21 m and the calculated water content at that transition is 0 6 0 1 these findings imply that the whole temperate ice layer is from 3 to 4 times softer than the cold ice and consequently that realistic ice flow models of polythermal glaciers should include the effect of water content on viscosity

the influence of snow cover thickness on the thermal regime of tete rousse glacier mont blanc range 3200 m a s l consequences for outburst flood hazards and glacier response to climate change 1 tete rousse glacier french alps was responsible for an outburst flood in 1892 that devastated the village of st gervais le fayet close to chamonix causing 175 fatalities changes in the hydrothermal configuration of the glacier are suspected to be the cause of this catastrophic outburst flood in 2010 geophysical surveys of this glacier revealed a subglacial lake that was subsequently drained artificially the processes controlling the thermal regime of the glacier have been investigated on the basis of measurements and snow firn cover and heat flow models using meteorological data covering the last 200 years temperature measurements show a polythermal structure with subglacial water trapped by the cold lowest part of the glacier 2 c the modeling approach shows that the polythermal structure is due to temporal changes in the depth of the snow firn cover at the glacier surface paradoxically periods with negative mass balances associated with warmer air temperature tend to cool the glacier whereas years with colder temperatures associated with positive mass balances tend to increase the glacier temperature by increasing the firnpack depth and extent the thermal effect of the subglacial lake is evaluated and shows that the lake was formed around 1980 according to future climate scenarios modeling shows that the glacier may cool again in the future this study provides insights into the thermal processes responsible for water storage inside a small almost static glacier which can lead to catastrophic outburst floods such as the 1892 event or potentially dangerous situations as in 2010

wave field migration as a tool for estimating spatially continuous radar velocity and water content in glaciers 1 normal moveout velocity analysis can lead to significant overestimates of the velocity structure of temperate glaciers since most englacial reflectors approximate point scatters and violate the assumption of planar flat lying reflectors migration velocity analysis mva is a tool that does not depend on the assumption of flat lying reflectors mva can provide laterally and vertically continuous velocity estimates from conventional common offset radar sections in a study of temperate bench glacier alaska we used mva coupled with dielectric modeling to estimate the distribution of water content along a cross section of the glacier we found the glacier has two layers an upper layer with relatively low water content and lower layer with relatively high water content the ability to quantify hydrostratigraphy is important in understanding water storage and routing within glaciers

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

detection of a subglacial lake in glacier de tete rousse mont blanc area france the processes that form intraglacial lakes are poorly understood because of the difficulty in detecting and assessing such hidden lakes extensive geophysical surveys were performed between 2007 and 2010 in order to reassess the risk of an outburst flood from glacier de tete rousse where outburst flooding from an intraglacial lake caused 175 fatalities in 1892 our geophysical survey combined ground penetrating radar measurements and nuclear magnetic resonance imaging we found a subglacial water filled reservoir with a volume of 55 000 m 3 artesian outpourings occurred when the subglacial cavity was reached by two borehole drillings indicating that the hydrostatic water pressure exceeded the ice pressure at the bottom of the cavity on the basis of these geophysical and glaciological findings we warned the public authorities in july 2010 of the risk facing the 3000 inhabitants downstream of the glacier the subglacial reservoir was drained artificially this example demonstrates how geophysical surveys can be used to detect this type of hazard when it is suspected in particular when no hydraulic outlet from the snout exists numerous ice temperature measurements have shown that the tongue of this glacier is cold based this thermal regime could explain the accumulation of water in this glacier

recharge of a subglacial lake by surface meltwater in northeast greenland observations of rapid persistent elevation gains that occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater during the summer melt period in greenland show that surface meltwater may be trapped and stored at the bed of an ice sheet affecting ice dynamics downstream the discovery of a 70 metre deep collapse basin near the summit of the largest and most northerly peripheral ice cap of greenland and the use of high resolution stereo satellite imagery to monitor its evolution suggests that surface meltwater can be trapped and stored beneath the greenland ice sheet previously meltwater from the surface of the ice sheet had been assumed to drain efficiently through the basal hydrologic system during the summer melt period rapid persistent elevation gains occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater and stored at least on annual time scales these findings have potential implications for our understanding of ice sheet temperature and velocity in a warming climate surface meltwater production on large ice sheets is expected to increase if this water is delivered to the ice sheet base it may have important consequences for ice dynamics for example basal water distributed in a diffuse network can decrease basal friction1 2 and accelerate ice flow3 4 5 6 7 8 whereas channelized basal water can move quickly to the ice margin where it can alter fjord circulation and submarine melt rates9 10 less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets here we show that a subglacial lake in greenland drained quickly as seen in the collapse of the ice surface and then refilled from surface meltwater input we use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the flade isblink ice cap in northeast greenland during the autumn of 2011 a collapse basin about 70 metres deep and about 0 4 cubic kilometres in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord over the next two years rapid uplift of the floor of the basin which is approximately 8 4 square kilometres in area occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice11 and alter downstream ice dynamics12 13 heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate

on the use of dispersive apvo gpr curves for thin bed properties estimation theory and application to fracture characterization the presence of a thin layer embedded in any formation creates complex reflection patterns caused by interferences within the thin bed the generated reflectivity amplitude variations with offset have been increasingly used in seismic interpretation and more recently tested on ground penetrating radar gpr data to characterize nonaqueous phase liquid contaminants phase and frequency sensitivities of the reflected signals are generally not used although they contain useful information the present study aims to evaluate the potential of these combined properties to characterize a thin bed using gpr data acquired along a common midpoint cmp survey carried out to assess velocity variations in the ground it has been restricted to the simple case of a thin bed embedded within a homogeneous formation a situation often encountered in fractured media dispersive properties ofthe dielectric permittivity of investigated materials homogeneous formation thin bed are described using a jonscher parameterization which permitted study of the dependency of amplitude and phase variation with offset apvo curves on frequency and thin bed properties filling nature aperture in the second part we discuss and illustrate the validity of the thin bed approximation as well as simplify assumptions and make necessary careful corrections to convert raw cmp data into dispersive apvo curves two different strategies are discussed to correct the data from propagation effects a classical normal moveout approach and an inverse method finally the proposed methodology is applied to a cmp gpr data set acquired along a vertical cliff it allowed us to extract the characteristics of a subvertical fracture with satisfying resolution and confidence the study motivates interest to use dispersion dependency of the reflection coefficient variations for thin bed characterization

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

finding the buried record of past earthquakes with gpr based palaeoseismology a case study on the hope fault new zealand in places where sedimentation and erosion compete at fast rates part of the record of past earthquakes on faults may be buried hence hidden in the first few metres below the surface we developed a novel form of palaeoseismology of geophysical type based on the use of a dense pseudo 3 d ground penetrating radar gpr survey to investigate such possible buried earthquake traces on a long fast slipping strike slip fault hope fault new zealand at a site terako where marked alluvial conditions prevail we first used lidar data to analyse the ground surface morphology of the 2 km2 site at the greatest resolution nineteen morphological markers were observed mainly alluvial terrace risers and small stream channels that are all dextrally offset by the fault by amounts ranging between 3 and 200 m the measurements document about 10 past earthquake slip events with a mean coseismic slip of 3 3 1 m with the most recent earthquake event having a slip of 3 0 5 m we then investigated a detailed area of the site 400 x 600 m2 with pseudo 3 d gpr we measured 56 similar to 400 m long 510 m spaced gpr profiles 250 mhz parallel to the fault and evenly distributed on either side the analysis revealed the existence of a palaeosurface buried at about 3 m depth corresponding to the top of alluvial terraces of different ages that buried surface is incised by a dense network of stream channels that are all dextrally offset by the fault we measured 48 lateral offsets in the buried channel network more than twice than at the surface these offsets range between 6 and 108 m as observed at the surface yet provide a more continuous record of the fault slip the similarity of the successive slip increments suggests a slip per event averaging 4 4 1 m fairly similar to that estimated from surface data from the total surface and buried 67 offset collection we infer that a minimum of 30 large earthquakes have broken the hope fault at the terako site in the last about 67 kyr with an average coseismic slip of 3 2 1 m a minimum average recurrence time of about 200 yr and a magnitude of at least mw 7 07 4 our study therefore confirms that part of the record of past earthquakes may indeed reside in the first few metres below the surface where it may be explored with geophysical gpr based palaeoseismology developing such a new palaeoseismological tool should provide rich information that may complement surface observations and help to document the past earthquakes on faults

mechanisms of subglacial cavity filling in glacier de tete rousse french alps the deadliest outburst flood from an englacial cavity occurred on glacier de tete rousse in the mont blanc area french alps in 1892 a subglacial reservoir was discovered in the same glacier in 2010 and drained artificially in 2010 2011 and 2012 to protect the 3000 inhabitants downstream the mechanism leading to the spontaneous refilling of the cavity following these pumping operations has been analyzed for this purpose the subglacial water volume changes between 2010 and 2013 were reconstructed the size of the cavity following the pumping was found to have decreased from 53 500 m 3 in 2010 to 12 750 m 3 in 2013 creep and the partial collapse of the cavity roof explain a large part of the volume loss analysis of cavity filling showed a strong relationship between measured surface melting and the filling rate with a time delay of 4 6 hours a permanent input of 15 m 3 d 1 not depending on surface melt was also found the meltwater and rain from the surface is conveyed to bedrock through crevasses and probably through a permeable layer of rock debris at the glacier bed the drainage pathway permeability was estimated at 0 054 m s 1 from water discharge measurements and dye tracing experiments

origin of the outburst flood from glacier de tete rousse in 1892 mont blanc area france extensive field measurements and historical data have been used to re analyse the cause of the outburst flood from glacier de tete rousse that devastated the village of saint gervais le fayet french alps in 1892 causing 175 fatalities the origin of this disaster was the rupture of an intraglacial cavity in glacier de tete rousse that released 200 000 m 3 of water and ice all previous studies have concluded that the intraglacial cavity was formed from a crevasse that was filled and enlarged by meltwater the re analysis presented here suggests that the reservoir of the upper cavity did not originate as an enlarging crevasse the origin of the meltwater reservoir was more likely a supraglacial lake formed before 1878 during a period of negative mass balance following a period of positive mass balance after 1878 the lake was hidden until the outburst flood of 1892 this means that such hazards may be detected by checking regularly for the formation of a lake on the surface of the glacier before it is hidden

delineation of a complexly dipping temperate glacier bed using short pulse radar arrays we have defined the complex bed topography for a section of a small temperate glacier using 50 mhz monostatic short pulse radar data and a synthetic aperture array processing method the data were collected on a 100 m by 340 m array grid in the upper stem of gulkana glacier central alaska u s a the array processing was based on a modified three dimensional 3 d kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping sub arrays to generate depth images in vertical planes typical sub array beam patterns are generally 5 at the 6 db level giving a flashlight like searching capability without distorting the wavelet shape the bed topography was constructed using normal reflections picked from 3 d array depth images in some instances reflections were imaged outside the data coverage area the bed surface dips steeply both parallel and transverse to the direction of ice flow the maximum observed depth is roughly 140 m the 3 d method resolved bed dips up to 45 in regions of steepest dip it improved depth accuracy by 36 compared with raw data and by 15 compared with standard two dimensional 2 d migration over 12 db of signal to noise improvement and improved spatial resolution was achieved compared to raw data and 2 d migration false bottom layering seen in the raw data and in 2 d migrations is not observed in the 3 d array results furthermore loss of bottom reflections is shown by the 3 d migration to be attributable to the dip and curvature of the reflector and not scattering losses or signal clutter from englacial inclusions

seasonal changes in ground penetrating radar signature observed at a polythermal glacier bylot island canada in recent years ground penetrating radar gpr has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers the geophysical method is able to exploit the dielectric difference between water air sediment and ice allowing delineation of subsurface hydrological thermal and structural conditions more recent gpr research has endeavoured to examine temporal change in glaciers in particular the distribution of the cold ice zone at polythermal glaciers however the exact nature of temporal change that can be identified using gpr has not been fully examined this research presents the results of three gpr surveys conducted over the course of a summer ablation season at a polythermal glacier in the canadian arctic a total of approximately 30 km of gpr profiles were collected in 2002 repeatedly covering the lower 2 km of stagnation glacier bylot island 72 58 n 78 22 w comparison between profiles indicated changes in the radar signature including increased noise appearance and disappearance of englacial reflections and signal attenuation in the latter survey further an area of chaotic returns in up glacier locations which was interpreted to be a wet temperate ice zone showed marked recession over the course of the ablation season combining all the temporal changes that were detected by gpr results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body including the drainage of 17 000 m 3 of temporarily stored intra glacial meltwater it is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity copyright 2006 john wiley sons ltd

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

calculation of glacier volume from sparse ice thickness data applied to schaufelferner austria in order to develop and evaluate a method for the determination of glacier volume from ice thickness data the volume of schaufelferner austria is calculated 1 by manual interpolation of ground penetrating radar gpr data based on measurements at 36 locations in 1995 2 by manual interpolation of 144 gpr measurements acquired for a higher resolution estimate in 2003 and 2006 3 by multiplying the mean of the measured ice thickness data by the glacier area 4 by automatic kriging of the 1995 gpr data and 5 by application of area volume scaling algorithms to the austrian glacier inventory data of 1969 1997 and 2006 the so determined glacier volumes are compared with the ice volume changes calculated from digital elevation models dems of the austrian glacier inventories the manually interpolated volumes based on the 1995 and 2003 06 gpr data yielded a volume loss only slightly different from volume loss calculated from the glacier inventories of 1997 and 2007 other methods were not able to reproduce the volume losses of the glacier inventory dems to assess the accuracy of deriving ice thickness changes with gpr repeated ice thickness measurements at the same locations were carried out between 2005 and 2008

ground penetrating radar and surface nuclear magnetic resonance monitoring of an englacial water filled cavity in the polythermal glacier of tete rousse in polythermal glaciers specific climatic topographic and exposure conditions may lead to the formation of englacial lakes that can produce catastrophic effects downstream in the event of abrupt natural drainage we have determined how a combination of ground penetrating radar gpr and surface nuclear magnetic resonance snmr surveys helped to locate and visualize the evolution of a water filled cavity within the tete rousse glacier french alps we have used gpr results to delineate the roof of the cavity and monitor the cavity deformation caused by artificial drainage because the glacier bed and cavity have complex 3d geometries we needed dense acquisition lines and 3d gpr views to qualitatively identify out of plane reflections this 3d approach made it possible to establish a precise map of the glacier bed topography the accuracy of which was verified against borehole observations then repetitive gpr measurements were used to obtain a quantitative estimate of the vertical deflection of the cavity s roof and changes in crevasse geometry observed in response to the decrease in the water pressure when 47 800 m3 of water was drained by pumping we have used 3d snmr imaging to locate water accumulation zones within the glacier and to estimate the volume of accumulated water the snmr monitoring revealed that in two years the cavity lost approximately 73 of its initial volume with 65 lost after the first drainage knowledge of the water contained in the ice provided a better understanding of gpr images and thus a more reliable interpretation of gpr data however snmr imaging had a much lower resolution in comparison with gpr and consequently gpr allowed a more accurate study of the evolution of cavity geometry caused by consecutive drainage and refilling this study demonstrated the value of combining gpr data with snmr data for the study of polythermal glaciers

full resolution 3d gpr imaging noninvasive 3d ground penetrating radar gpr imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface full resolution imaging requires unaliased recording of reflections and diffractions coupled with 3d migration processing the gpr practitioner can easily determine necessary acquisition trace spacing on a frequency wavenumber f k plot of a representative 2d gpr test profile quarter wavelength spatial sampling is a minimum requirement for full resolution gpr recording an intensely fractured limestone quarry serves as a test site for a 100 mhz 3d gpr survey with 0 1 m 0 2 m trace spacing this example clearly defines the geometry of fractures in four different orientations including vertical dips to a depth of 20 m decimation to commonly used half wavelength spatial sampling or only 2d migration processing makes most fractures invisible the extra data acquisition effort results in image volumes with submeter resolution both

short pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of matanuska glacier alaska u s a wavelets transmitted by short pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of matanuska glacier alaska u s a the field studies were in the ablation region where radar horizons could at some point be identified with interfaces between clear ice and air water or basal ice and were performed in early spring before drainage fully developed the profiles usedclosely spaced antennas with bandwidths centered near 50 and 400 mhz transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts migration and fourier transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections interfacial dielectric contrasts are determined from the relative phase of the wavelets near the terminus lake some basal ice events above 8 m depth are interpreted as voids further up glacier most englacial events are interpreted as voids but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids water or debris phase cannot be determined for the basal substrate transition reflections recommendations are made for improving the wavelet recovery process and the quality of gpr migration

imaging glacial sediment inclusions in 3 d using ground penetrating radar at kongsvegen svalbard the quiescent phase surge type glacier kongsvegen flows confluent with the continuously fast flowing kronebreen in northwestern spitsbergen the lower regions of kongsvegen overlie glaciomarine sediments which have been incorporated into the ice during multiple surge events the resulting englacial structures are exposed at the surface and on a cliff section these structures have variously been interpreted as thrusts formed by compression or sediment filled crevasses formed by extension we collected a grid of closely spaced ground penetrating radar profiles in the area adjacent to the cliff section several structures were imaged in 3 d including a strong subhorizontal basal reflector which was underlain by a second weaker subhorizontal reflector the basal reflector was occasionally reverse faulted suggesting compression clear englacial features extended upwards from it dipping up glacier at angles of 40 and steepening towards the glacier surface they had complex geometries that changed rapidly cross glacier the structures were orientated at 30 to ice flow suggesting modification by lateral compression from kronebreen some of these englacial structures clearly crossed the basal reflector we conclude that the englacial features imaged are not likely to be derived from crevasse filling and were probably formed by thrusting the results contribute to our understanding of surge initiation and termination processes and interpretation of features in the palaeorecord copyright 2009 john wiley sons ltd

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd

englacial water distribution in a temperate glacier from surface and borehole radar velocity analysis we have obtained common offset common midpoint cmp and borehole vertical vrp ground penetrating radar profiles close to the margin of falljokull a small steep temperate valley glacier situated in southeast iceland velocity analysis of cmp and vrp surveys provided a four layered velocity model this model was verified by comparison between the depths of englacial reflectors and water channels seen in borehole video and from the depths of boreholes drilled to the bed in the absence of sediment within the glacier ice radar velocity is inversely proportional to water content using mixture models developed by paren and looyenga the variation of water content with depth was determined from the radar velocity profile at the glacier surface the calculated water content is 0 23 0 34 velocity 0 166 m ns 1 which rises sharply to 3 0 4 1 velocity 0 149 m ns 1 at 28 m depth interpreted to be the level of the piezometric surface below the piezometric surface the water content drops slowly to 2 4 3 3 velocity 0 152 m ns 1 until 102 m depth where it falls to 0 09 0 14 velocity 0 167 m ns 1 the water content of the ice then remains low to the glacier bed at about 112 m these results suggest storage of a substantial volume of water within the glacier ice which has significant implications for glacier hydrology ice rheology and interpretations of both radar and seismic surveys