radio echo sounding studies of englacial water movement in variegated glacier alaska une crue glaciaire du variegated a ete enregistree a l aide d un emetteur mono impulsion de 3mhz les discontinuites intraglaciaires ont ete observees dans le domaine des 12 a 30 mhz les changements dans la forme des echos sont interpretes en terme de redistribution de l eau dans les canaux glaciaires et les cavites reliees au lit a quelque distance a l aval

internal reflecting horizons in spitsbergen glaciers a single pronounced internal reflecting horizon has been observed on radio echo sounding from over 30 glaciers in spitsbergen they are often present along the entire length of the glacier remaining at a fairly constant depth 100 200 m below the ice surface echo strength data from radio echo sounding have been used to obtain reflection coefficients for these horizons of between 15 and 25 db combined with results of ice core studies the possible causes of this internal layer are investigated the presence of water is found to be the most likely explanation indicating the existence at depth of a layer of temperate ice

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

radio echo sounding of svalbard glaciers peculi arities of radio echo sound ing of mountain gl aciers and ice fields between nunataks from terrestria l vehicles and from heli copters are consi dered in this paper the possibility of using compar atively high frequen cies of up to 865 mhz for sounding suc h glaciers is demonst rated on the basis of expe rimental data results of airbo rne radio echo so unding of svalba rd gl aciers of various types dimensions and regime obtained with the help of the 620 m hz airbo rne equipment of high resolution are shown returns from the gla cier bed have been obtained on the majority of glaciers unde r in vestigation the firn regions of ice fields with temp erate regimes flowing between nuna taks are mostly an exception depre ssion in the glacier bed with the ice thic kne ss up to 540 m as well as int ernal reflecting boundaries have been detected in some glaciers ic e volum es of glaciers have been determined from the airborne radio echo sounding data with the use of a parabolic appr oximation to the cross section glacier profiles good correl ational dependence between ice volume and surface area of glaciers has been established and is use d to estimate the ic e and water resources in sva lbard glaciers

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

fault slip and seismic moment of the 1700 cascadia earthquake inferred from japanese tsunami descriptions 1 the 1700 cascadia earthquake attained moment magnitude 9 according to new estimates based on effects of its tsunami in japan computed coseismic seafloor deformation for hypothetical ruptures in cascadia and tsunami modeling in the pacific ocean reports of damage and flooding show that the 1700 cascadia tsunami reached 1 5 m heights at seven shoreline sites in japan three sets of estimated heights express uncertainty about location and depth of reported flooding landward decline in tsunami heights from shorelines and post 1700 land level changes we compare each set with tsunami heights computed from six cascadia sources each source is vertical seafloor displacement calculated with a three dimensional elastic dislocation model for three sources the rupture extends the 1100 km length of the subduction zone and differs in width and shallow dip for the other sources ruptures of ordinary width extend 360 670 km to compute tsunami waveforms we use a linear long wave approximation with a finite difference method and we employ modern bathymetry with nearshore grid spacing as small as 0 4 km the various combinations of japanese tsunami heights and cascadia sources give seismic moment of 1 9 1022 n m equivalent to moment magnitude 8 7 9 2 this range excludes several unquantified uncertainties the most likely earthquake of moment magnitude 9 0 has 19 m of coseismic slip on an offshore full slip zone 1100 km long with linearly decreasing slip on a downdip partial slip zone the shorter rupture models require up to 40 m offshore slip and predict land level changes inconsistent with coastal paleoseismological evidence

shallow groundwater response to rainfall on a forested headwater catchment in northern coastal california implications of topography rainfall and throughfall intensities on peak pressure head generation the pore water pressure head that builds in the soil during storms is a critical factor for the prediction of potential slope instability we report findings from a 3 year study of pressure head in 83 piezometers distributed within a 13 ha forested catchment on the northern coast of california the study s primary objective was to observe the seasonal and storm based dynamics of pressure head at a catchment scale in relation to observed rainfall characteristics and in situ topography to better understand landscape patterns of pressure head an additional goal was to determine the influence of the interaction between rainfall and forest canopy in altering delivery of water and pressure head during the large storms necessary to induce landsliding we found that pressure head was highly variable in space and time at the catchment scale pore pressures peaked close to maximum rainfall intensity during the largest storms measured the difference between rainfall and throughfall delivered through the canopy was negligible during the critical landslide producing peak rainfall periods pore pressure was spatially variable within the catchment and did not strongly correlate with surficial topographic features only 23 of the piezometers located in a variety of slope positions were found to be highly responsive to rainfall topographic index statistically explained peak pressure head at responsive locations during common storms but not during the larger storms with potential to produce landslides drainage efficiency throughout the catchment increased significantly in storms exceeding 2 to 7 months peak pressure head return period indicated by slowing or cessation of the rate of increase of pressure head with increasing storm magnitude this asymptotic piezometric pattern persisted through the largest storm measured during the study faster soil drainage suppressed pressure head response in larger storms with important process implications for pore pressure development and landslide hazard modelling copyright 2012 john wiley sons ltd

characterization of englacial channels by ground penetrating radar an example from austre broggerbreen svalbard 1 ground penetrating radar profiles at 100 mhz have been collected over an englacial channel system on the cold ice glacier austre broggerbreen svalbard analysis and synthetic modeling of the travel times and waveforms of the reflections from the channel have shown that after a near vertical drop of 45 m in a moulin the watercourse flows 900 m subhorizontally the size of the conduit varies from a large semicircular channel 5 m wide at its base close to the moulin to a vertically elongated 2 5 m high channel close to the outlet variations in the depth of water along the channel have been calculated to be between 14 and 90 of the channel height using detailed analysis of waveforms the low channel gradient 2 and results of dye tracing experiments suggest that there is a significant degree of ponding along the channel length this channel geometry was probably created during a period of increased crevassing from the little ice age a descent into the moulin provided direct observations of the channel dimensions close to the moulin and helped verify the interpretations and conclusions drawn from the study thus radar reflections can be successfully used to determine the depth dimensions and water content of englacial watercourses due to the transparency of ice to radar signals and the strong contrast in velocity between water ice and air this technique offers exciting possibilities for the remote monitoring of englacial channels from the glacier surface

geocryological processes linked to high arctic proglacial stream suspended sediment dynamics examples from bylot island nunavut and spitsbergen svalbard recent research has identified differences in processes contributing to suspended sediment concentration ssc dynamics in proglacial streams between high arctic and alpine catchments but does not examine processes explicitly linked to the periglacial environment three glacierized basins were studied austre broggerbreen and midre lov enbreen svalbard 79 n 12 e and glacier b28 unofficially named stagnation glacier bylot island nunavut 73 n 78 w ssc variations were modelled from continuous turbidity discharge and meteorological data throughout the summer months three statistical tools were utilized principal component analysis changepoint analysis and multivariate regression these are shown to be effective in identifying subperiods of distinctive geocryological and glaciofluvial characteristics multivariate regression for the subseasons included autoregressive integrated moving average modelling and showed that ssc variations were related not only to discharge variability but also to fluctuations in energy fluxes the results are interpreted in terms of spatio temporal changes in sediment mobilization and supply associated with changes in the relative importance of fluvial glacial and periglacial processes this evidence supports the notion of important linkages between glacial fluvial and periglacial systems but exemplifies distinct variability between high arctic glaciers copyright 2005 john wiley sons ltd

topographic controls on shallow groundwater dynamics implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment hydrologic connectivity is regarded as one of the key controls in determining catchment rainfall run off response and has been linked to the export of solutes from uplands to streams we sought to identify the patterns of hydrologic connectivity within a small forested watershed by monitoring the shallow groundwater fluctuations of simple topographically defined landform sequences footslope backslope shoulder a spatially distributed instrument network was employed to continuously measure hydrometric responses of the shallow subsurface during seasonal wet up from summer through winter in a small till mantled research catchment we demonstrate that the spatial patterns of shallow water table extent and duration and therefore hydrologic connectivity had a strong seasonal signature during the low antecedent soil moisture conditions typically associated with the growing season water tables were patchy discontinuous and only the wettest near stream footslope areas were consistently hydrologically connected with the stream network during the dormant season footslopes and backslopes maintained water tables that persisted between storm events and were almost continuously connected with the stream network in the largest storm events the typically driest landforms shoulder slopes established shallow transient water tables suggesting that nearly the entire catchment was temporarily hydrologically connected with the stream network in addition we found significant differences p 0 05 in the magnitude and duration of groundwater responses to rainfall among landform groups both seasonally and during events these results have implications for using a similarity approach in representing characteristic hydrologic responses of topographically defined watershed elements determining hydrologic connectivity between watershed elements as well as for understanding solute transport in catchments copyright 2010 john wiley sons ltd

glacier hydrology in svalbard norwegian high arctic abstract progress in glacier hydrology has focused on temperate glaciers although partly or wholly non temperate glaciers are found in many parts of the world and significant areas of former ice sheets were probably non temperate it has usually been assumed that drainage from non temperate glaciers consists of relatively dilute and invariable supraglacial runoff in this paper the hydrology of glaciers in the high arctic archipelago of svalbard is examined variations in the thermal regimes of glaciers and their implications for drainage are first addressed results from svalbard concerning meltwater discharge and storage and solute and suspended sediment dynamics are then reviewed in general meltwater penetration of non temperate ice is limited and drainage from non temperate glaciers in svalbard has many of the characteristics of sub aerial drainage however it would be erroneous to view this drainage simply as dilute supraglacial runoff as significant material transport occurs in suspension and solution furthermore twentieth century climate change has probably led to changes in the thermal regimes of some svalbard glaciers such that relict drainage structures are sometimes observed while meltwater yields are augmented by runoff which can be attributed to the loss of mass from glaciers at large spatial scales turbid plumes observed at the marine margins of polythermal ice caps indicate that meltwater can be routed subglacially through non temperate ice

soil saturation patterns in steep convergent hill slopes under forest and pasture vegetation the relationships between hillslope form and the development of zones of hillslope saturation are central to studies of process hydrology these relationships are examined in two small steep 30 first order basins under forest and pasture vegetation hillslope saturation patterns are described using a probability analysis of observations of peak water table elevations made at individual sites in each basin in both first order basins the effects of topographic convergence on the spatial variability of hillslope saturation zones are most pronounced on shallow slopes and in steeper areas where hillslope form is strongly concave the implications of vegetation type on the formation and variation of hillslope saturation are also examined the differences in hillslope saturation patterns in each vegetation type are attributed primarily to differences in net rainfall and not soil physical properties or other features of topography

the hydrochemistry of meltwaters draining a polythermal based high arctic glacier south svalbard i the ablation season solute and runoff time series at finsterwalderbreen svalbard provide evidence for considerable basal routing of water and the existence of at least two contrasting subglacial chemical weathering environments the hydrochemistry of a subglacial upwelling provides evidence for a snowmelt fed subglacial reservoir that dominates bulk runoff during recession flow high concentrations of cl and crustal ions high pco2 and ratios of so2 4 so2 4 hco 3 close to 0 5 indicate the passage of snowmelt through a subglacial weathering environment characterized by high rock water ratios prolonged residence times and restricted access to the atmosphere at higher discharges bulk runoff becomes dominated by icemelt from the lower part of the glacier that is conveyed through a chemical weathering environment characterized by low rock water ratios short residence times and free contact with atmospheric gases these observations suggest that icemelt is routed via a hydrological system composed of basal ice marginal englacial and supraglacial components and is directed to the glacier margins by the ice surface slope upwelling water flows relatively independently of icemelt to the terminus via a subglacial drainage system possibly constituting flow through a sediment layer cold basal ice at the terminus forces it to take a subterranean routing in its latter stages the existence of spatially discrete flow paths conveying icemelt and subglacial snowmelt to the terminus may be the norm for polythermal based glaciers on svalbard proglacial mixing of these components to form the bulk meltwaters gives rise to hydrochemical trends that resemble those of warm based glaciers these hydrochemical characteristics of bulk runoff have not been documented on any other glacier on svalbard to date and have significance for understanding interactions between thermal regime and glacier hydrology 1998 john wiley sons ltd

the flow of a polythermal glacier mccall glacier alaska u s a we have analyzed the flow of polythermal mccall glacier in arctic alaska using measurements of surface velocity from the 1970s and 1990s together with measurements of ice thickness and surface slope we have investigated both the present flow and seasonal and long term flow variations our analysis of the present flow reveals that i longitudinal stress coupling is important along the entire length of the glacier and ii there is significant basal sliding beneath a 2 km long section of the lower glacier this sliding exists year round and it accounts for more than 70 of the total motion there we have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up glacier from it both effects are reflected in the observed surface profile of mccall glacier the longitudinal stress coupling length of mccall glacier is three times the ice thickness almost twice that typical of temperate glaciers this is a direct effect of lower strain rates which themselves are associated with the smaller mass balance gradients of arctic and continental glaciers long term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution this means that long term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small seasonally velocities reach their annual minimum in spring and increase during the short summer melt season by up to 75 above mean winter values however the extra motion associated with the period of elevated velocities is only about 5 of the total annual motion the speed up is due to an increase in basal sliding this implies that most of the glacier bed is at the melting point the zone affected by the melt season speed up extends well up glacier of any moulins or other obvious sources for meltwater at the bed

the 1 5 ka varved record of lake montcortes southern pyrenees ne spain abstract the karstic lake montcortes sedimentary sequence spanning the last 1548 yr constitutes the first continuous high resolution multi proxy varved record in northern spain sediments consist of biogenic varves composed of calcite organic matter and detrital laminae and turbidite layers calcite layer thickness and internal sub layering indicate changes in water temperature and seasonality whereas the frequency of detrital layers reflects rainfall variability higher temperatures occurred in lake montcortes in ad 555 738 825 875 1010 1322 and 1874 present lower temperatures and prolonged winter conditions were recorded in ad 1446 1598 1663 1711 and 1759 1819 extreme and multiple precipitation events dominated in ad 571 593 848 922 987 1086 1168 1196 1217 1249 1444 1457 1728 1741 and 1840 1875 indicating complex hydrological variability in ne spain since ad 463 the sedimentary record of lake montcortes reveals a short term relation between rainfall variability and the detrital influx pronounced during extended periods of reduced anthropogenic influences in pre industrial times during warm climate episodes population and land use increased in the area after the onset of the industrialization the relationship between climate and human activities decoupled and population dynamics and landscape modifications were therefore mostly determined by socio economic factors

how to model shallow water table depth variations the case of the kervidy naizin catchment france the aim of this work is threefold 1 to identify the main characteristics of water table variations from observations in the kervidy naizin catchment a small catchment located in western france 2 to confront these characteristics with the assumptions of the topmodel concepts and 3 to analyse how relaxation of the assumptions could improve the simulation of distributed water table depth a network of piezometers was installed in the kervidy naizin catchment and the water table depth was recorded every 15 min in each piezometer from 1997 to 2000 from these observations the kervidy naizin groundwater appears to be characteristic of shallow groundwaters of catchments underlain by crystalline bedrock in view of the strong relation between water distribution and topography in the bottom land of the hillslopes however from midslope to summit the water table can attain a depth of many metres it does not parallel the topographic surface and it remains very responsive to rainfall in particular hydraulic gradients vary with time and are not equivalent to the soil surface slope these characteristics call into question some assumptions that are used to model shallow lateral subsurface flow in saturated conditions we investigate the performance of three models topmodel a kinematic model and a diffusive model in simulating the hourly distributed water table depths along one of the hillslope transects as well as the hourly stream discharge for each model two sets of parameters are identified following a monte carlo procedure applied to a simulation period of 2649 h the performance of each model with each of the two parameter sets is evaluated over a test period of 2158 h all three models and hence their underlying assumptions appear to reproduce adequately the stream discharge variations and water table depths in bottom lands at the foot of the hillslope to simulate the groundwater depth distribution over the whole hillslope the steady state assumption topmodel is quite constraining and leads to unacceptable water table depths in midslope and summit areas once this assumption is relaxed kinematic model the water table simulation is improved a subsequent relaxation of the hydraulic gradient diffusive model further improves water table simulations in the summit area while still yielding realistic water table depths in the bottom land

radio echo sounding of spitsbergen glaciers problems in the interpretation of layer and bottom returns comparaison des sondages de glaciers du spitsbezg par un equipement 60 mhz spri mk iv et des sondages sovietiques sur 440 et 620 mhz les fortes differences observees sont attribuees a la forte absorption et grande dispersion sur le lit rocheux des sondages sovietiques

on the thermal regime of an arctic valley glacier a study of white glacier axel heiberg island n w t canada from 1974 to 1981 a total of 32 bore holes was drilled on white glacier and vertical ice temperature profiles measured the data obtained allowed the construction of three longitudinal and four transverse profiles of the two dimensional temperature distributions thus an extensive layer of temperate or near temperate ice was discovered close to the bedrock in the lowest part of the glacier tongue it was also found that the temperature distribution cannot be in a steady state since there is a temperature minimum 100 150 m below the glacier surface in the accumulation area a simple numerical model calculation shows that this minimum can be mostly explained by the general climatic warming since 1880 the 10 m temperatures show diffuse relations to climatic conditions and balance zones a simple scheme for extrapolating surface temperatures is discussed

comparison of radio echo sounding 30 1000 mhz and high resolution borehole temperature measurements at finsterwalderbreen southern spitsbergen svalbard

effects of digital elevation model map scale and data resolution on a topography based watershed model the effects of digital elevation model dem map scale and data resolution on watershed model predictions of hydrologic characteristics were determined for topmodel a topography based watershed model the effects of topography on watershed hydrology are represented in topmodel as the distribution of ln a tan b where ln is the napierian logarithm a is the upslope area per unit contour length and tan b is the gravitational gradient the minimum maximum mean variance and skew values of the ln a tan b distribution were computed from 1 24 000 scale 24k dems at 30 and 90 m resolutions and from 1 250 000 scale 250k dems at 90 m resolution for 71 areas in pennsylvania new york and new jersey an analysis of topmodel showed that model predictions of the depth to the water table the ratio of overland flow to total flow peak flow and variance and skew of predicted streamflow were affected by both the dem map scale and data resolution further topmodel analyses showed that the effects of dem map scale and data resolution on model predictions were due to the sensitivity of the predictions to the mean of the ln a tan b distribution which was affected by both dem map scale and data resolution dem map scale affected the mean of the ln a tan b distribution through its influence on the mean of the ln a distribution which characterizes land surface shape and the mean of ln 1 tan b distribution which characterizes land surface slope dem resolution in contrast affected the mean of the ln a tan b distribution primarily by its influence on the mean of the ln a distribution

borehole drainage and its implications for the investigation of glacier hydrology experiences from haut glacier d arolla switzerland studies of glacier hydrology rely increasingly on measurements made in boreholes as a basis for reconstructing the character and behaviour of subglacial drainage systems in temperate glaciers in which boreholes remain open to the atmosphere following drilling the interpretation of such data may be complicated by supraglacial or englacial water flows to and from boreholes we report on a suite of techniques used to identify borehole water sources and to reconstruct patterns of water circulation within boreholes at haut glacier d arolla switzerland results are used to define a number of borehole drainage types examples of each drainage type are presented along with the manner in which they influence interpretations of borehole water levels borehole water quality data and borehole dye traces the analysis indicates that a full understanding of possible borehole drainage modes is required for the correct interpretation of many borehole observations and that those observations provide an accurate indication of subglacial conditions only under relatively restricted circumstances copyright 2001 john wiley sons ltd

saturation regions in catchments and their relations to soil and topographic properties abstract criteria are derived for the existence of saturated areas on draining hillslopes in natural catchments these are given in terms of soil transmissivity the hillslope gradient and its wetness state characterised by the baseflow discharge from the catchment analyses are made for idealised hillslopes with uniform soils to obtain expression for the width of the saturated zone the size of saturated zones on undulating hillslopes with gradiational soils is shown to depend strongly on topographic convergence or divergence the effects of soil transmissivity hillslope geometry and drainage flux density are lumped into a dimensionless parameter whose value determines the location of seepage boundaries on slopes of specified geometry scaling relations for seepage area in catchments of different size are shown to be generally nonlinear and depend primarily on local hillslope gradients relative predictions of seepage zone size are confirmed by observed hydrographs from three catchments with different physical characteristics

observations and modeling of hillslope throughflow temperatures in a coastal forested catchment a growing body of research on stream thermal regimes has highlighted the importance of heat advection associated with surface water and groundwater interactions such as hyporheic exchange groundwater discharge and hillslope throughflow inputs existing catchment models that predict stream temperature use a variety of approaches to estimate throughflow temperatures but none has been evaluated against field measurements of throughflow temperature in this study throughflow temperatures were monitored over two winters at 50 locations adjacent to a headwater stream 11 ha catchment area located in the rain on snow zone of the pacific northwest existing approaches to estimate throughflow temperature under or overpredicted throughflow temperatures by up to 5 c or were unable to represent the influence of transient snow cover therefore a conceptual parametric model that is computationally efficient was developed that simulates hillslope hydrology and throughflow temperatures the model structure includes an upslope reservoir that drains into a downslope reservoir that in turn drains into the stream vertical and lateral energy and water fluxes are simulated using simplified process representations the model successfully predicts throughflow temperatures and highlights the dominant role of throughflow advection and the influence of snow cover on stream thermal regimes during high flow periods and rain on snow events

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

storm runoff processes in a small forested drainage basin a brief review was made of storm runoff processes and the mechanisms of its generation in relation to subsurface water behaviors in a small forested drainage basin located in the western suburbs of tokyo japan the results of field investigations showed that the main source of storm runoff was groundwater flow and that the rapid and large amounts of groundwater discharge during a storm event could not be explained solely by the traditional concept of darcian matrix flow several mechanisms such as pipe flow air pressure effect and capillary barrier effect were recognized that would induce a rapid response of groundwater to storm events depending on differences in local hydrologic conditions all of these mechanisms were chiefly attributed to inhomogeneities of the soil deposits the importance of dynamic behaviors of subsurface water during a storm event was emphasized in considering the mechanism of storm runoff generation

glacial hydrological system characterization using ground penetrating radar hydrological systems near the terminus of a high arctic glacier and a proglacial icing on bylot island canada were investigated using ground penetrating radar gpr the ice thickness and the location and depth of tunnels within the glacier and icing were imaged modelling of the gpr response was utilized to predict the data quality and to assist in its interpretation the unique properties of the ice enabled velocity determinations from the diffraction patterns generated by point source reflectors as well as traditional velocity surveys the propagation velocity of the radar pulses through the ice depended on the air and water content in the ice the identification of drainage tunnels was attained through pulse polarity analysis and interpolation between the profiles in gridded surveys it was found that reflectivity analysis may enable gpr to be used for acquiring three dimensional information on the thermal structure of glaciers the much more complicated structure of the icing was imaged with higher frequency antennae and it was found that general ice types could be mapped using radar stratigraphical analysis both buried slush mounds and subsurface channel fills were identified within the icing a portion of the icing near the centre of the valley floor that has persisted perennially for over 50 years was found to be sitting on a slightly higher area of the valley bottom and thus was not subjected to the same hydrothermal erosional forces as the edges of the icing setting up a feed back loop encouraging the preservation of the central core of ice and promoting the destruction and rebuilding of the edges every year

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

basal debris entrainment and transport in glaciers of southwestern bylot island canadian arctic abstract glaciers on southwestern bylot island in the canadian arctic flow from an alpine setting in high grade crystalline archean terrane on to coastal lowlands underlain by clastic sedimentary

anisotropic radio wave scattering from englacial water regimes mýrdalsjokull iceland colinear polarized 5 mhz radar profiling data were obtained on m rdalsjokull a temperate glacier in iceland radar transects and therefore polarization planes were aligned approximately parallel transverse and oblique to the ice flow direction echoes from the shallower half to two thirds of the ice were 10 20db stronger on the oblique and longitudinal transects than those on the transverse transects anisotropy as a function of depth is clearly seen at the sites where the transects cross strong scattering on longitudinal transects apparently caused extinction of a radar reflecting layer that was continuously profiled on the transverse transects a radio wave scattering model shows that scattering from a longitudinal water filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo we conclude that low frequency mhz radio waves can help to characterize englacial water regimes

relations between topography and water table depth in a shallow forest soil the relations between water table depth in a shallow forest soil and topographic characteristics derived from a raster digital elevation model dem were studied water table depths at times of observation and peak levels between times of observation were measured weekly during an autumn winter rainy season at 59 wells in a catchment ca 0 04 km 2 drained by an ephemeral stream located 80 km east of vancouver canada digital elevation models with grid spacings of 4 8 and 16 m were derived from a ground survey and values of a upslope contributing area per unit contour length tan surface slope and x a measure of surface curvature were computed from the dems to avoid problems with data censoring when the water table dropped below the bottom of some wells the depths were discretized into classes and discriminant analysis was used to relate water table depth classes to the topographic indices the relations were derived using data from 30 wells and were tested on data from the other 29 wells to provide an independent test of predictive capability the index in a tan provided more reliable classifications than a multiple discriminant analysis using in a tan and x as separate predictor variables water table depths at some wells were consistently misclassified e g 0 3 correct classifications whereas at others they were classified correctly in up to 100 of cases consistent misclassification at individual wells could reflect either the effects of errors in the derived topographic indices through errors in the dem or the algorithms used to calculate the indices or phenomena not related to surface topography such as variability in soil properties or differences between the surface topography and the topography of the base of the soil profile the predictive accuracy and statistical significance of derived relations decreased as the dem grid size increased from 4 to 8 to 16 m these results are valid only for predictions of water table depths at points further research should explore the effect of grid scale on relations between grid averaged water table depths and topographic indices and on methods to parameterize subgrid scale variability

interpretation of radio echoes from storglaciaren northern sweden analyse des echos d ondes metriques et decimetriques a l aide d une theorie d onde scalaire de la diffraction et d une statistique simple on peut par exemple etudier les rugosites du lit et les orientations des diffuseurs a l interieur de la glace

evolution of the internal drainage system in the lower part of the ablation area of storglaci aren sweden during the 1989 melt season ten tracer experiments were conducted to investigate seasonal diurnal and spatial variations in the internal drainage system in the ablation area of storglaciaren sweden dye was injected into moulins and dye concentration and discharge were monitored in two streams at the glacier terminus sydjakk and nordjakk dye emerged only in sydjakk transit velocities ranged from 0 07 to 0 29 m s implying that drainage was through a well defined conduit system velocity and discharge relations suggest that these conduits are part of a multi branched arborescent network of individually braided wide low passages a progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits presumably including a decrease in the degree of braiding and an increase in size the system reached its late season configuration in early august by which time the energy dissipated by the flowing water would have sufficed to melt between 0 7 and 21 m 3 of ice per meter of conduit length depending on conduit size potential closure rates exceed melt rates on conduit walls throughout most of the drainage system and so conduits are probably full of water during periods of higher daily discharge with water pressures exceeding atmospheric pressure variations in tracer return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding in this case resulting from drowning of low divides between channels as discharge increases

velocity of radio waves in glaciers as an indicator of their hydrothermal state structure and regime the results of measurements of radio wave velocities rwv by wide angle reflection war methods in the temperate abramov glacier in the alai mountain ridge and the two layered sub polar fridtjovbreen and hansbreen on svalbard using a low frequency 2 13 mhz radar are considered and discussed the experimental data obtained and the data from the literature show that the values of rwv could be a good indicator of the hydrothermal state of glaciers as such these data enable the identification of cold temperate and transitional two layered glaciers and can be used for estimation of the water content in glaciers and changes in the hydrothermal state

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

factors influencing the basal temperatures of a high arctic polythermal glacier a number of glaciers in the canadian high arctic are composed primarily of cold ice but the ice at or near their beds reaches the pressure melting point pmp in the ablation zone past modelling studies have suggested that the basal temperatures of some of these glaciers reach the pmp where they should not indicating that they are not in thermal equilibrium with present day surface air temperatures to investigate the possible reasons for thermal disequilibria in such glaciers a two dimensional ice temperature model was used to simulate the inferred thermal characteristics of john evans glacier ellesmere island results indicate that while surface refreezing and historical ice thickness changes have had a warming effect upon basal ice temperatures supraglacial meltwater reaching the glacier bed provides the single most critical heat source for explaining the apparent thermal disequilibrium between present day inferred ice bed temperatures and those modelled under present day boundary conditions

throughflow variability on a forested hillslope underlain by compacted glacial till this study examined the spatial and temporal variability of throughflow in a shallow forest oil in terms of the controls exerted by topography soil properties and the shape of the water table hillslope outflow was measured at nine troughs installed at a road cut and hydraulic head was measured at 37 piezometers installed to the confining till surface at the base of the soil at the lowest flows the distribution of throughflow across the hillslope conformed reasonably to the distribution of upslope contributing area computed from the topography of the confining basal till layer at higher flows however the distribution of throughflow shifted partly as a result of changes in the orientation in flow tubes as the piezometric surface changed at high flows surface topography appeared to provide a reasonable proxy for the shape of the water table shunting of water through discrete macropores however can apparently overwhelm topographic controls on throughflow at least for slope widths less than about 10 m effective hydraulic conductivities computed at the scale of the troughs varied over two orders of magnitude and displayed no consistent relationship with the thickness of the saturated layer estimates at the plot scale c 10 m hillslope width were far less variable and for higher flows displayed an approximately linear relationship with saturated zone thickness copyright 2000 john wiley sons ltd

detecting and characterising an englacial conduit network within a temperate swiss glacier using active seismic ground penetrating radar and borehole analysis englacial hydrology plays an important role in routing surface water to the glacier s bed and it consequently affects the glacier s dynamics however it is often difficult to observe englacial conduit conditions on temperate glaciers because of their short lived nature we acquired repeated active surface seismic data over the rhone glacier switzerland to monitor and characterise englacial conduit conditions amplitude versus angle analysis suggested that the englacial conduit is water filled and between 0 5 and 4 m thick a grid of gpr profiles acquired during the 2018 melt season showed the englacial conduit network persisting and covering 14 000 m 2 in late summer 2018 several boreholes were drilled into the conduit network we observed generally stable water pressure but there were also short sudden increases a borehole camera provided images of a fast flowing englacial stream transporting sediment through the conduit from these observations we infer that the englacial conduit network is fed by surface meltwater and morainal streams the surface and morainal streams merge together enter the glacier subglacially and flow through subglacial channels along the flank these subglacial channels flow into highly efficient englacial conduits traversing the up glacier section of the overdeepening before connecting with the subglacial drainage system

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

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

fluvial suspended sediment transport from cold and warm based glaciers in svalbard an analysis of temporal variability in proglacial suspended sediment concentration is undertaken using time series data collected from three svalbard basins which include one largely cold based glacier austre broggerbreen one largely warm based glacier finsterwalderbreen and one intermediate polythermal glacier erdmannbreen the temporal variability in proglacial suspended sediment concentration is analysed using multiple regression techniques in which discharge is supplemented by other predictors acting as surrogates for variability in sediment supply at diurnal medium term and seasonal timescales these multiple regression models improve upon the statistical explanation of suspended sediment concentration produced by simple sediment rating curves but need to account for additional stochastic elements within the time series before they may be considered successful an interpretation of the physical processes which are responsible for the regression model characteristics is offered as a basis for comparing the different arctic glaciofluvial suspended sediment transport systems with that of their better known temperate glaciofluvial counterparts it is inferred that the largely warm based glacier is dominated by sediment supply from subglacial reservoirs which evolve in a similar manner to temperate glaciers and which cause a pronounced seasonal exhaustion of suspended sediment supply the largely cold based glacier however is dominated by sediment supply from marginal sources which generate a responsive system at short time scales but no significant seasonal pattern the intermediate polythermal glacier basin which was anticipated to be similar to the warm based glacier instead shows a highly significant seasonal increase in suspended sediment supply from an unusual subglacial reservoir emerging under pressure in the glacier foreland the temperate model of glaciofluvial suspended sediment transport is therefore found to be of limited use in an arctic context copyright 1999 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