surface and bed topography of trapridge glacier yukon territory canada digital elevation models and derived hydraulic geometry measurements of ice thickness and surface elevation are prerequisite to many glaci ological investigations a variety of techniques has been develo ped for inter pret ation of these data including means of constructing regularly gridded digital eleva tion models dem s for use in numcrical studies here we present a simple yet stati sti cally sound method for processing ice pe netr ating radar data and descr ibe a tech nique for interpol ating these data onto a regular grid dems generatcd fort rapridge glacier yukon territory canada are used to derive geometric quantities lhal give pre liminary insights into the underlying basin scale hydrol ogical syste m this simple geo metric analysis suggests that at low water press ures a dendrilic drainage netw ork exists that evolves into a uniaxial morphology as water pressure approaches notation these pre dictions are compared to hydraulic connection probabilities based on bore hole drilling

magnetospheric substorms and nighttime height changes of the f2 region at middle and low latitudes using the published plots of 15 min interval values of h f2 the minimum virtual height of the ionospheric f2 region at five japanese stations spread over 26 45 n 15 35 n geomagnetic and 128 142 e it is shown that there are frequent rapid increases and less frequent decreases of h f2 by 100 200 km in about 2 hours with near simultaneous start and end at all five stations in the postmidnight hours and at three to five stations in the premidnight hours in the months of september and december 1988 and march 1989 about 80 h f2 perturbations of the above type are identified the near simultaneity of the h f2 disturbances at the five stations suggests that an plasma drift due to an east west electric field is the cause of the h f2 disturbances this interpretation is validated by showing that there is a simultaneous presence of bay disturbances in auroral latitude magnetograms over a wide longitude range during almost all the h f2 increases it is shown that neutral wave disturbances propagating equatorward even with a speed of 750 m s cannot account for the h f2 disturbances the study reveals two categories of h f2 perturbations 1 h f2 increases starting near the beginning of the geomagnetic negative bays at auroral latitudes and 2 rapid h f2 increases starting near the maximum intensity phase of the auroral bays and preceded by h f2 decreases starting at the onset time of the bay disturbance or a little earlier using the vast amount of h f2 data collected all over the globe it is possible to quantify and characterize the substorm related electric fields and their variabilities such characterization is very useful in understanding the magnetospheric and the magnetosphere ionosphere interaction processes involved in the generation of magnetospheric substorms it is also pointed out that the understanding of f2 region changes during magnetic storms may improve greatly if the large f2 region changes caused by electric fields on the substorm time scale are taken into account the h f2 disturbances reported in this study are similar in time scale and appearance to the h f2 disturbances caused by long period atmospheric waves and this suggests the possibility of a mixup of the two effects and the consequent wrong identification on some occasions

hydrological characteristics of the drainage system beneath a surging glacier a rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers outburst floods from the subglacial lake grimsvotn in iceland took place before during and after surging of skei ararjokull the glacier beneath which the outburst floods drain the observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non surge phases during surge conditions basal water is dispersed slowly across the bed in a distributed drainage system but when the glacier is not surging water is transported rapidly through a system of tunnels

modeling subglacial water routing at paakitsoq w greenland 1 the functioning of the greenland ice sheet s subglacial drainage system and its effect on ice dynamics have been inferred largely from hypothetical hydrology dynamics models and from analysis of satellite data and in situ gps measurements despite this there is still uncertainty about how the surface hydrology interacts with the subglacial drainage system and affects basal water pressures and ice flow especially over annual time scales to address this we developed a high spatial 100 m and temporal 1 h resolution distributed physically based subglacial hydrological model and applied it to the paakitsoq region western greenland the model is driven with moulin input hydrographs calculated by a surface routing and lake filling draining model forced ultimately with distributed hourly runoff calculated by a surface mass balance model key outputs from the model are spatially and temporally varying subglacial water pressures and proglacial stream hydrographs early in the melt season short spikes in water pressure lasting less than a day occur as a result of lake drainage events during midsummer there are sustained periods of high water pressure lasting days to weeks even at times when the subglacial system is inferred to be predominantly efficient later in the summer large diurnal fluctuations in water pressure occur with peaks regularly exceeding ice overburden pressure superimposed on a gradually declining trend these phenomena support the results of previous hypothetical modeling efforts and inferences drawn from gps measurements

drainage system development in consecutive melt seasons at a polythermal arctic glacier evaluated by flow recession analysis and linear reservoir simulation 1 the drainage systems of polythermal glaciers play an important role in high latitude hydrology and are determinants of ice flow rate flow recession analysis and linear reservoir simulation of runoff time series are here used to evaluate seasonal and inter annual variability in the drainage system of the polythermal finsterwalderbreen svalbard in 1999 and 2000 linear flow recessions are pervasive with mean coefficients of a fast reservoir varying from 16 1999 to 41 h 2000 and mean coefficients of an intermittent slow reservoir varying from 54 1999 to 114 h 2000 drainage system efficiency is greater overall in the first of the two seasons the simplest explanation of which is more rapid depletion of the snow cover reservoir coefficients generally decline during each season at 0 22 h d 1 in 1999 and 0 52 h d 1 in 2000 denoting an increase in drainage efficiency however coefficients do not exhibit a consistent relationship with discharge finsterwalderbreen therefore appears to behave as an intermediate case between temperate glaciers and other polythermal glaciers with smaller proportions of temperate ice linear reservoir runoff simulations exhibit limited sensitivity to a relatively wide range of reservoir coefficients although the use of fixed coefficients in a spatially lumped model can generate significant subseasonal error at finsterwalderbreen an ice marginal channel with the characteristics of a fast reservoir and a subglacial upwelling with the characteristics of a slow reservoir both route meltwater to the terminus this suggests that drainage system components of significantly contrasting efficiencies can coexist spatially and temporally at polythermal glaciers

changes in geometry and subglacial drainage derived from digital elevation models unteraargletscher switzerland 1927 97 digital elevation models of the bed and surface of unteraargletscher switzerland are used to reconstruct the theoretical pattern of basal water drainage for the years 1927 1947 1961 and 1997 during which period the glacier was thinning and receding the theoretical drainage pattern for 1997 compares well in a broad sense with the locations of active moulins and the hydraulic connection status of boreholes drilled to the glacier bed changes in the basal water flow pattern over the period 1927 97 that are revealed by the theoretical reconstructions of the subglacial drainage system structure are likely to have resulted from changes in glacier geometry concurrent with the retreat and thinning of the glacier the height of medial moraines increased probably due to the insulating effect of the debris cover reducing the melt of the underlying ice this increase of moraine heights has led to the formation of hydraulic barriers at the glacier bed such that water flow has become channelized beneath the ice along drainage axes that parallel the course of the medial moraines on the glacier surface

temporal variations in flow velocity at finsterwalderbreen a svalbard surge type glacier inter and intra annual velocity variations are well known on alpine glaciers but their importance for arctic glaciers has only been recognized more recently this paper presents flow velocity data from finsterwalderbreen a 35 km 2 polythermal surge type glacier in southern svalbard that is presently 100 years into its quiescent phase field measurements of glacier surface velocities are available from 1950 52 and 1994 97 and mean velocities for the last decade are estimated for the lower glacier using cables drilled to the glacier bed these velocities show substantial seasonal variations indicating that basal sliding is an important component of surface velocities and interannual fluctuations of up to 75 possibly indicating variations in subglacial water storage several lines of evidence indicate that this glacier has an extensive subglacial hydrological system generally considered to be a prerequisite for surge type glaciers which is at least partly pressurized information on surface morphology from 1898 onwards shows that the glacier has experienced continuous retreat since the last surge in about 1910 and has now retreated 1 5 km further back than its previous pre surge position in 1898 tracking of moraine loops on terrestrial and aerial photographs acquired over a 100 year period indicates that the surge period of finsterwalderbreen may be lengthening in response to climate changes

on the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady state conditions this however is not necessarily the case where discharges are larger than a few tens of liters per second and the down glacier slope of the bed is more than a few degrees the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice as a result the pressure in such tunnels may normally be atmospheric or possibly even at the triple point pressure if there is no open connection to the glacier surface simple calcu lations suggest that such pressures in subglacial conduits may be more common than herclofore anticipated the positions of such open conduits may be unstable to small per turbations in discharge or ice veloci ty this is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice cond ui ts can thus trend diago nally across the direction of ice aow if an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of he conduit more mechanical energy will become available resulting in a positive feedback process subglacial channels at atmospheric pressure may inauence the origin and morphology of certain glacial landforms such as eskers and plastically molded features resume sur le role de l inergie newtonnienne dam le maintien du riseau aquiflrl sous glaciaire cl la pression almosph irique de recentes etudes theoriques d hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn pletement rempli d eau en condition d cquil ibre stable ceci neanmoins n est pas necess airement le cas lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente du lit du glacier est superieure a quelques degres i energie potentielle mise en oeuvre par i eau descendant celle pente peut ire capable de fondre les parois d un chenal sous glaciaire beaucoup plus vite que le chenal ne peut se refermer par le auage plastique de la glace il en resuhe que la pression dans de tels chenaux peut nor rnalement etre atrnospherique

a new regional high resolution map of basal and surface topography for the greenland ice sheet margin at paakitsoq west greenland in 2005 an airborne survey was carried out from a twin otter aircraft at pakitsup akuliarusersua paakitsoq near ilulissat in west greenland the survey aimed to measure ice thickness with a 60 mhz coherent radar and surface elevation with a scanning laser altimeter positioning information came from multiple on board differential gps units and an inertial navigation system the region surveyed covers 80 km along the ice margin and has a total area of 2700 km 2 with varying density of measurements the between track distance was 1 km near the margin increasing to 3k m away from the margin regional high resolution maps of basal topography under the greenland ice sheet are useful for resolving important glaciological and hydrological questions and for enhancing related process studies such as the influence of basal meltwater on ice dynamics the ice sheet margin in this region is also currently under consideration for hydropower development and has a long and continuing history of glaciological investigations lately with emphasis on the connection between surface meltwater formation and surface velocity of the ice sheet here we present a new regional map of the surface and basal topography of the ice sheet margin and discuss some of the implications for reported observations at swiss camp

spatio temporal variability in elevation changes of two high arctic valley glaciers uncertainties in estimates of glacier and ice cap contribution to sea level rise exist in part due to poor quantification of mass balance errors particularly those resulting from extrapolation of sparse measurements centre line data are often assumed to be representative of the glacier as a whole with little attention paid to extrapolation errors or their effect on mass balance estimates here we present detailed digital elevation model dem measurements of glacier wide elevation changes over the last 40 years at two glaciers on svalbard norwegian arctic austre broggerbreen and midtre lovenbreen are shown to have lost 27 54 0 98 and 9 65 0 76 10 7 m 3 of ice respectively between 1966 and 2005 findings that we relate to trends in average summer air temperatures and winter accumulation these volume losses correspond to geodetic balances of 0 58 0 03 and 0 41 0 03 m w e a 1 respectively our analysis revealed high spatial complexity in patterns of elevation change varying between glaciers between measurement intervals and within and between elevation bins balances from extrapolated centre line geodetic data were the same within errors as those from full coverage dem differencing in the majority of comparisons yet significantly underestimated balance in three instances additionally field mass balance from centre line ablation stake data underestimated balances from full coverage geodetic measurements during three of six measurement periods these findings may support the hypothesis that field measurements under estimate svalbard glacier mass loss at least partly as a result of the failure of centre line measurements to account for glacier wide variations in ablation our results demonstrate the importance of deriving accurate interpolation functions and constraining extrapolation errors from sparse measurements

structure morphology and water flux of a subglacial drainage system midtdalsbreen norway digital elevation models of the surface and bed of midtdalsbreen norway are used to calculate subglacial hydraulic potential and infer drainage system structure for a series of subglacial water pressure assumptions ranging from atmospheric to ice overburden a distributed degree day model is used to calculate the spatial distribution of melt on the glacier surface throughout a typical summer which is accumulated along the various drainage system structures to calculate water fluxes beneath the glacier and exiting the portals for the different water pressure assumptions in addition 78 dye tracing tests were performed from 33 injection sites and numerous measurements of water discharge were made on the main proglacial streams over several summer melt seasons comparison of the calculated drainage system structures and water fluxes with dye tracing results and measured proglacial stream discharges suggests that the temporally and spatially averaged steady state water pressures beneath the glacier are 70 of ice overburden analysis of the dye return curves together with the calculated subglacial water fluxes shows that the main drainage network on the eastern half of the glacier consists of a hydraulically efficient system of broad low channels average width height ratio 75 the smaller drainage network on the west consists of a hydraulically inefficient distributed system dominated by channels that are exceptionally broad and very low average width height ratio 350 the even smaller central drainage network also consists of a hydraulically inefficient distributed system dominated by channels that are very broad and exceptionally low average width height ratio 450 the channels beneath the western and central glacier must be so broad and low that they can essentially be thought of as a linked cavity system

interannual variability in the spatial distribution of winter accumulation at a high arctic glacier finsterwalderbreen svalbard and its relationship with topography glacier mass balance and hydrology are strongly influenced by the distribution of snow accumulation at the start of the melt season two successive end of winter snow cover surveys at finsterwalderbreen svalbard are here used to investigate the interannual variability in the spatial distribution of accumulation and its relationship with topography 40 62 of the variance in snow depth was not determined by elevation assessed by linear regression of snow depth on surface elevation which could not therefore necessarily be used as a sole predictor of the spatial distribution of accumulation here principal components pc analysis of the topographic variables elevation slope north south and east west aspects shows that only two of six pcs determined for 2 years sampling locations had maximum loadings on altitude aspect was more important with maximum loadings on four pcs hierarchical cluster analysis was then applied to these pcs significant correlations with accumulation in each of two terrain clusters were given by 1 elevation and slope 2 east west aspect only 1999 1 elevation only 2 no significant correlations 2000 there is strong interannual variability not only in the magnitude of winter accumulation 0 41 m w e in 1999 0 58 m w e in 2000 but also in its spatial distribution and its relationship with topography

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

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

controls on the basal water pressure in subglacial channels near the margin of the greenland ice sheet assuming a channelized drainage system in steady state we investigate the influence of enhanced surface melting on the water pressure in subglacial channels compared to that of changes in conduit geometry ice rheology and catchment variations the analysis is carried out for a specific part of the western greenland ice sheet margin between 668 n and 66830 0 n using new high resolution digital elevation models of the subglacial topography and the ice sheet surface based on an airborne ice penetrating radar survey in 2003 and satellite repeat track interferometric synthetic aperture radar analysis of european remote sensing satellite 1 and 2 ers 1 2 imagery respectively the water pressure is calculated up glacier along a likely subglacial channel at distances of 1 5 and 9 km from the outlet at the ice margin using a modified version of rothlisberger s equation our results show that for the margin of the western greenland ice sheet the water pressure in subglacial channels is not sensitive to realistic variations in catchment size and mean surface water input compared to small changes in conduit geometry and ice rheology

assessing the future evolution of meltwater intrusions into a mine below gruvefonna svalbard meltwater intrusions of glacial origin complicate the operation of a coalmine situated approximately 200 m below the bed of gruvefonna ice cap svalbard the magnitude of this water input is expected to increase with the intended enlargement of the mine the current praxis evacuation of the water by pumping is an expensive undertaking and prompts the investigation of alternative solutions the evaluation of different options requires reliable values of the total volume and the input rate of the water to be drained to quantify the melt rate at the glacier surface we applied a distributed temperature index model the model parameters were calibrated using mass balance measurements performed at gruvefonna during the 2003 ablation season the water discharge in the mine during the same period was derived from records of the pump rate comparing the records of modelled melt and measured discharge reveals an efficient hydraulic connection between the glacier surface and the mine the total discharge volume in the mine over the 2003 melt season was about 2 8 10 6 m 3 exceeding significantly the total melt and rainwater production on the glacier surface directly above the mine 1 2 10 6 m 3 this implies that the mine discharge receives contributions from a larger surface area based on the distribution of hydraulic potential at the glacier bed we estimate this contributing area in a number of scenarios we calculate the amount of meltwater intrusions for several steps of the planned mine enlargement

ground water intrusions in a mine beneath hoganesbreen svalbard assessing the possibility of evacuating water subglacially evacuation of the ground water intruding into a coal mine beneath ho ganesbreen svalbard is difficult and expensive to solve this problem it was proposed thatthe minebeconnectedtotheice bedrock interface pumpinghot waterfromthe mine should establish a flow path along the glacier bed where the ground water would drain gravitationally in this paper we assess the requirements for maintaining such a drainage system in open channel conditions to obtain the bedrock topography we determined the ice thickness by ground penetrating radar and subtracted it from the surface elevation measured by global positioning system a measured temperature profile at the site where themineshouldconnecttotheglacierbed 140mdepth revealedthatthebasal iceisbelow thepressure melting point thelocations of majorsubglacialconduitswereestimatedusing ahydraulic potentialapproach weadoptedamodeloftime dependentdischargethrougha ro thlisberger channel to calculate a set of scenarios using different flow law parameters resultsofthesimulationssuggestthatforthegivenconditions waterflow wouldbepressur ized thereby inhibiting the gravitational drainage of the mine

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

rerouting of subglacial water flow between neighboring glaciers in west greenland investigations of the greenland ice sheet s subglacial hydrological system show that the connectivity of different regions of the system influences how the glacier velocity responds to variations in surface melting here we examine whether subglacial water flow paths can be rerouted beneath three outlet glaciers in the ablation zone of western greenland we use lamont doherty and center for remote sensing of ice sheets of university of kansas cresis ice penetrating radar data to create a new ice thickness map we then use a simple subglacial water flow model to examine whether flow paths can be rerouted and identify the topographic conditions that are sensitive to subglacial rerouting by varying water pressures within an observationally constrained range we show that moderate changes in pressure can cause flow paths to reroute and exchange water from one subglacial catchment to another flow across subglacial overdeepenings is particularly sensitive to rerouting these areas have low hydraulic gradients driving flow so subtle water pressure variations have a strong influence on water flow direction based on correlations between water flow paths and ice velocity changes we infer that water piracy between neighboring catchments can result in a different spatial pattern of hydrologically induced ice velocity speedup depending on the amount and timing of surface melt the potential for subglacial water to reroute across different catchments suggests that multiple hydrographs from neighboring glaciers are likely necessary to accurately ascertain melt budgets from proglacial point measurements the relationship between surface runoff ice dynamics and proglacial discharge can be altered by rerouting of subglacial water flow within and across outlet glaciers

determining the extent of pressurized flow beneath storglaciaren sweden using results of tracer experiments and measurements of input and output discharge two experiments were conducted on the drainage system beneath the lower part of the ablation zone of storglaciaren a small valley glacier in northern sweden in the first experiment over 70 tracer tests were performed in a cluster of moulins during a 1 month period at sub daily intervals in the second experiment input and output discharge signals were measured on the supraglacial melt stream emptying into a moulin and on the proglacial stream to which the moulin drains the data from these two experiments are used in an idealized model of the subglacial drainage system to calculate the percentage of the system flowing as an open channel results from the tracer experiment suggest that the system is pressurized to within 60 340 m of the snout while analysis of the discharge data indicates pressurized conduits to within 0 415 m of the snout

evaluation of sand waves in an estuary the bella williamson rate of sediment turnover organic content of sediment rst ocs dissection plane method integrates relevant physical chemical and biological analyses in order to estimate the chronic impacts of dredging on estuarine ecosystems a spectral analysis by a finite fourier transform of estuarine sand waves is presented which only requires a spatial sand wave record that is relatively easy to measure in contrast to stochastic analyses which require both spatial and temporal observations of sand wave profiles the total energy content or equivalently the statistical variance of the spatial sand wave profile and the equilibrium subrange of the wave number spectrum provide readily observable measures of the rst in an estuary economic savings promise to be significant in addition a uniform 3 power law for the wave number equilibrium subrange is presented which offers an opportunity to obtain a sand wave frequency spectrum without a temporal sand wave profile record through a dispersion transformation proportional to the bed shear velocity

subglacial drainage system structure and morphology of brewster glacier new zealand a global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of brewster glacier these are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure pw i pw ice overburden ii pw half ice overburden iii pw atmospheric additionally 16 dye tracing experiments at 12 locations were performed through a summer melt season dye return curve shape together with calculations of transit velocity dispersivity and storage are used to infer the likely morphology of the subglacial drainage system taken together the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden by mid summer water pressures are closer to half ice overburden and the channelised drainage system is more hydraulically efficient surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system copyright 2008 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

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

mapping of a hydrological ice sheet drainage basin on the west greenland ice sheet margin from ers 1 2 sar interferometry ice radar measurement and modelling

the rate of chemical weathering beneath a quiescent surge type polythermal based glacier southern spitsbergen svalbard glacierized basins in the high arctic are believed to be regions of low chemical weathering rates despite the lack of pertinent data because it is believed that water does not flow in significant quantities through subglacial drainage systems we have calculated chemical weathering rates at finsterwalderbreen a polythermal surge type glacier in svalbard rates of 320 and 150 meq m 1 year 1 were measured in 1994 and 1995 respectively the corresponding water fluxes were 4 1 10 7 and 1 7 10 7 m 3 we estimate that we have measured 72 of the total annual discharge hence the true annual chemical weathering rates are 440 and 210 meq m 2 year 1 respectively this gives a mean annual chemical weathering rate of 330 meq m 2 year 1 which approximates the continental average of 390 meq m 2 year 1 and is intermediate between chemical weathering rates measured on cold based glaciers 110 160 meq m 2 year 1 and temperate glaciers 450 1000 meq m 2 year 1 this suggests that there may be a direct link between chemical weathering rates and thermal regime and that glacierized basins in the high arctic cannot necessarily be considered as regions of low chemical weathering and co 2 drawdown

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