character of the englacial and subglacial drainage system in the upper part of the ablation area of storglaciaren sweden on 4 july 1986 dye was injected at a point slightly above the equil ibrium line on storglac iliren a small valley glacier in northern sweden just below the equilibrium line the glacier bed is over deep ened the dye re appeared in a stream at the glacier terminus over the next 35 d this stream normally carries relatively little sediment in constrast to the situ ation in another nearby stream that also emerges from the glacier this sugge sts that the dye traveled in englacial rather than subglacial conduits tracer tests utilizing salt in bore holes in the overde epening support this interp retation as the bore holes were draining well above the bed the dye appeared during three distinct events suggesting that it became divided into at least three separate parcels shortly after iojection this probably occurred in the crevassed area in the vicinity of the inje ction point the englacial location of the drainage may be explained by the fact that in order to remain at the pressure melting p oint water in subg lacial conduits coming out of the overde epening may have had to warm up faster than would be possible by visc ous heating alone such

rheology of till beneath storglaciaren sweden in order to study in situ the rheology of a deforming subglacial till various instruments were emplaced in till beneath storglaciaren sweden boreholes were used to gain access to the till beneath about 100 m of ice tiltmeters provided an estimate of the shear strain rate in the till two other instruments yielded measures of till strength in addition water pressures were recorded in boreholes and in the till a computer controlled distance meter provided an effectively continuous record of the surface velocity and data from frequent surveys of a stake network were used to estimate the mean basal drag based on a force balance calculation tilt rates varied directly with effective pressure so decreases in water pressure apparently increased the coupling between the glacier and the bed surface speed was either out of phase with tilt or varied independently of tilt thus increases in speed were apparently a consequence either of longitudinal coupling or of reduced coupling between the glacier and the bed they were not a result of till deformation till strength varied directly with effective pressure which is consistent with it being a mohr coulomb or frictional material the devices measuring till strength are presumed to have been pulled through the till at a speed that varied in phase with the surface speed but till strength did not vary systematically with surface speed this implies that the residual strength of the till is insensitive to strain rate thus the appropriate constitutive equation for till rheology may be of the form e e k where k is a constant this is consistent with experimental data reported in the geotechnical literature

is the north atlantic oscillation reflected in scandinavian glacier mass balance records the north atlantic oscillation nao is one of the modes of climate variability in the north atlantic region the atmospheric circulation during the winter season in this region commonly displays a strong meridional north south pressure contrast with low air pressure cyclone centred close to iceland and high air pressure anticyclone near the azores this pressure gradient drives the mean surface winds and the mid latitude winter storms from west to east across the north atlantic bringing mild moist air to northwest europe the nao index is based on the difference of normalised sea level pressures slp between ponta delgada azores and stykkisholmur iceland the slp anomalies at these stations are normalised by division of each monthly pressure by the long term 1865 1984 standard deviation interannual atmospheric climate variability in northwest europe especially over great britain and western scandinavia has during the last decades been attributed mainly to the nao causing variations in the winter weather over the northeast north atlantic and the adjacent land areas a comparison between the nao index and the winter december march precipitation between ad 1864 and 1995 in western norway shows that these are strongly linked correlation coefficient 0 77 variations in the nao index are also reflected in the mass balance records of glaciers in western scandinavia the nao index is best correlated with mass balance data from maritime glaciers in southern norway e g alfotbreen r 2 0 51 the record of holocene last ca 11 500 cal yr glacier variations of maritime glaciers in western scandinavia is thus a proxy of pre instrumental nao variations copyright 2000 john wiley sons ltd

stabilizing feedbacks in glacier bed erosion glaciers often erode transport and deposit sediment much more rapidly than nonglacial environments1 with implications for the evolution of glaciated mountain belts and their associated sedimentary basins but modelling such glacial processes is difficult partly because stabilizing feedbacks similar to those operating in rivers2 3 have not been identified for glacial landscapes here we combine new and existing data of glacier morphology and the processes governing glacier evolution from diverse settings to reveal such stabilizing feedbacks we find that the long profiles of beds of highly erosive glaciers tend towards steady state angles opposed to and slightly more than 50 per cent steeper than the overlying ice air surface slopes and that additional subglacial deepening must be enabled by non glacial processes climatic or glaciological perturbations of the ice air surface slope can have large transient effects on glaciofluvial sediment flux and apparent glacial erosion rate

large values of hydraulic roughness in subglacial conduits during conduit enlargement implications for modeling conduit evolution hydraulic roughness accounts for energy dissipated as heat and should exert an important control on rates of subglacial conduit enlargement by melting few studies however have quantified how subglacial conduit roughness evolves over time or how that evolution affects models of conduit enlargement to address this knowledge gap we calculated values for two roughness parameters the darcy weisbach friction factor f and the manning roughness coefficient n using dye tracing data from a mapped subglacial conduit at rieperbreen svalbard values of f and n calculated from dye traces were compared with values of f and n calculated from commonly used relationships between surface roughness heights and conduit hydraulic diameters roughness values calculated from dye tracing ranged from 75 0 97 for f and from 0 68 0 09 s m 1 3 for n equations that calculate roughness parameters from surface roughness heights underpredicted values of f by as much as a factor of 326 and values of n by a factor of 17 relative to values obtained from the dye tracing study we argue these large underpredictions occur because relative roughness in subglacial conduits during the early stages of conduit enlargement exceeds the 5 range of relative roughness that can be used to directly relate values of f and n to flow depth and surface roughness heights simple conduit hydrological models presented here show how parameterization of roughness impacts models of conduit discharge and enlargement rate we used relationships between conduit relative roughness and values of f and n calculated from our dye tracing study to parameterize a model of conduit enlargement assuming a fixed hydraulic gradient of 0 01 and ignoring creep closure it took conduits 9 25 days to enlarge from a diameter of 0 44 m to 3 m which was 6 7 fold longer than using common roughness parameterizations copyright 2013 john wiley sons ltd

holocene development and geomorphic processes at omnsbreen southern norway evidence for glacier permafrost interactions omnsbreen is a small 0 5 km2 and degrading glacier situated at the regional lower limit of present day permafrost distribution and glaciation at present the existence of omnsbreen is mainly de

evidence for a till layer beneath storglaciaren sweden based on electrical resistivity measurements evidence for a till layer beneath storglaciaren sweden based on electrical resistivity measurements

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice ii theory simple theory supports field observations lawson and others 1998 that subglacial water flow out of overdeepenings can cause accretion of layered debris bearing ice to the bases of glaciers the large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths if that flow ascends a sufficiently steep slope out of an overdeepening the water will supercool as the pressure melting point rises and basal ice accretion will occur diurnal occasional or annual fluctuations in water discharge will cause variations in accretion rate debris content of accreted ice or subsequent diagenesis producing layers under appropriate conditions net accretion of debris bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget

links between acceleration melting and supraglacial lake drainage of the western greenland ice sheet 1 the impact of increasing summer melt on the dynamics and stability of the greenland ice sheet is not fully understood mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding here we compare subdaily ice velocity and uplift derived from nine global positioning system stations in the upper ablation zone in west greenland to surface melt and supraglacial lake drainage during summer 2007 starting around day 173 we observe speedups of 6 41 above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations followed by a late summer slowdown after initial speedup we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting most lake drainages were undetectable in the velocity record and those that were detected only perturbed velocities for 1 day suggesting preexisting drainage systems could efficiently drain large volumes of water the dynamic response to melt forcing appears to 1 be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses and 2 decrease over the course of the summer presumably as the subglacial drainage system evolves to greater efficiency the relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here thus increases in summer melting may not guarantee faster seasonal ice flow

little ice age clearly recorded in northern greenland ice cores four ice cores drilled in the little investigated area of northern and northeastern greenland were evaluated for their isotopic 18o and chemical content from these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced which reveals distinct climate cooling during the 17th and the first half of the 19th century timing of the preindustrial temperature deviations agrees well with other northern hemisphere temperature reconstructions however their extent 1 c significantly exceeds both continental records as well as previous southern and central greenland ice core time series a 20 30 increase in the sea salt aerosol load during these periods supports accompanying circulation changes over the north atlantic comparison with records of potential natural climate driving forces points to an important role of the long term solar influence but to only episodically relevant cooling during years directly following major volcano eruptions

do debris covered glaciers demonstrate distinctive hydrological behaviour compared to clean glaciers abstract supraglacial debris is known to strongly influence the distribution of glacier surface melt since melt inputs drive the formation and evolution of glacial drainage systems it should follow that the drainage systems of debris covered glaciers will differ from those of debris free glaciers this would have implications for the proglacial runoff regime subglacial erosion and glacier dynamics this paper presents analysis of return curves from 33 successful dye injections into the extensively debris covered miage glacier italian alps it demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system where the debris cover is continuous melt is lower and the surface topography is chaotic with many small supraglacial catchments these factors result in an inefficient englacial subglacial drainage network beneath continuous debris which drains to the conduit system emanating from the upper ablation zone melt rates are high in areas of clean and dirty ice above the continuous debris runoff from these areas is concentrated by inter moraine troughs into large supraglacial streams which encourages the early season development of an efficient englacial subglacial conduit system downstream of this area drainage efficiency from the debris covered area increases over the melt season but dye trace transit velocity remains lower than from moulins on the upper glacier future runoff models should account for the influence of supraglacial debris on the hydrological system

modifications to the theory of intraglacial waterways for the case of subglacial ones on defend l idee que dans les glaciers de montagne temperes les voies d eau sont sous glaciaires pour un conduit noye sous glaciaire il faut introduire deux processus importants l accroissement de la deformation plastique sur les cotes amont des bosses et la chaleur apportee par l eau des sources qui en hiver rend compte de la plus grande partie du debit la theorie explique pourquoi rothlisberger 1972 dut adopter une valeur non realiste pour le parametre rheologique de la glace elle conduit a la conclusion que dans les zones non surcreusees la plus grande partie de l annee les conduits sous glaciaires doivent rester non noyes et a la pression atmospherique cas des surcreusements l incidence de ce nouveau modele sur la theorie du glissement des glaciers

greenland gisp2 ice core and historical indicators of complex north atlantic climate changes during the fourteenth century the paper uses greenland gisp2 ice core data together with historical documentary information to investigate the nature of climate changes that took place between ad 1270 and 1450 across the north atlantic region detailed deuterium and deuterium excess time series resolved to c 8 10 samples per year are used to reconstruct relative changes in greenland air temperature and past changes in sea surface tem perature across the western north atlantic the data show that sea surface temperatures during the late thirteenth century and the majority of the fourteenth century were characterized by relatively high amplitude warming and cooling events these changes preceded a marked reduction in the amplitude of the sea surface temperature changes c 30 40 years before the well known change in northern hemisphere tropospheric circulation characterized by a marked increase in regional storminess that started between c ad 1400 and 1420 the time interval between ad 1270 and 1450 also appears over greenland to have fea tured several short lived phases of marked air temperature lowering that were rarely ever equalled during succeeding centuries we believe that the climate changes described here are of considerable importance in understanding climate dynamics of the north atlantic region since they took place at a time when the north atlantic oscillation nao may have been weak the results also show that the marked change in atmospheric circulation coincident with a significant increase in north atlantic storminess at c ad 1400 1420 possibly the biggest such change in the holocene took place after the strong perturbations in north atlantic sea surface temperature both warming and cooling described here as well as after several episodes of air temperature lowering over greenland

hydrologic monitoring of supercooled meltwater from icelandic glaciers knowledge of how glaciers entrain sediment is central to understanding processes of glacier movement and products of glacial sediment deposition previous work has shown that if the total hydraulic potential of subglacial meltwater increases more rapidly than the resulting mechanical energy can be transformed into sensible heat then supercooling and ice growth will result this process causes frazil ice to grow onto adjacent glacier ice which acts to trap sediment in flowing meltwater eventually producing sedimentary inclusions within glacier ice supercooling has been recognised as a sediment entrainment mechanism at glaciers in alaska and more recently at several temperate icelandic glaciers here we present short period temperature measurements and field evidence of glaciohydraulic supercooling from three icelandic glaciers temperature measurements demonstrate that supercooling occurs over a range of hydrological conditions and that the process does not operate continuously at all instrumented sites measurements of supercooling during a small jokulhlaup are also presented progressive accretion of supercooled meltwater creates sediment laden ice exposures adjacent to active artesian vents understanding controls on the efficacy and pervasiveness of hydraulic supercooling is important for decoding the sedimentary record of modern and ancient glaciers and ice sheets

alpine subglacial hydrology abstract the size and shape of subglacial flow pathways exert a strong influence over the pressure and speed at which meltwaters are routed through glaciers these characteristics in turn influence glacier sliding velocity and the quantity and quality of bulk meltwaters discharging from glaciers in this paper we summarise four empirical research approaches that have been developed to improve our understanding of the subglacial hydrology of predominantly temperate based alpine glaciers investigations of bulk meltwater discharge and chemistry tracer studies proglacial bedrock investigations and borehole investigations as a result of linking these studies to conceptual or numerical models three arborescent and four non arborescent or distributed subglacial drainage configurations are described these drainage networks may be neither spatially nor temporally persistent but may compete with and replace each other on a seasonal basis a qualitative model of the temporal and spatial evolution of a typical alpine subglacial drainage system is advanced on the basis of research conducted at haut glacier d arolla switzerland

positive feedbacks associated with erosion of glacial cirques and overdeepenings the principal points of water input to a glacier are the bergschrund in cirques and crevasse fields lower on the glacier crevasse fields commonly occur over convexities at the heads of overdeepenings in glacier beds the amplitude of subglacial water pressure fluctuations is large just down glacier from these points of water input erosion by quarrying is likely in such areas erosion is thus inferred to be localized on the headwalls of cirques and overdeepenings in the case of overdeepenings this leads to a positive feedback process in which a perturbation in the bed causes crevassing at the surface resulting in erosional forces that accentuate the perturbation when subglacial water flows up an adverse bed slope leading out of a cirque or overdeepening much of the viscous energy dissipated is used to warm the water to keep it at the pressure melting temperature as the ice thins and the pressure decreases in such situations subglacial conduits are maintained by high water pressures rather than by melting of conduit walls in the limit water pressures apparently become so high that water is forced out along the ice bed interface and the conduits collapse the products of erosion are then no longer flushed out and a protective till layer accumulates by limiting erosion on such adverse bed slopes this till layer controls the geometry of these overdeepened basins

extrusion flow demonstrated by bore hole deformation measurements over a riegel storglaciaren sweden inclinometry measurements in a 126 m bore hole slightly down glacier from the crest of a riegel on storglaciaren showed what appears to be indisputable extrusion flow during the last 3 weeks of july 1984 the velocity at the bed was about five times that at the surface and lay in a direction deviating 50 60 from that at the surface the increase in velocity with depth began more than 50 m above the bed in august and the first half of september the flow returned nearly to normal with only a slight tendency toward extrusion the flow in july appeared to be related to a period of large diurnal water pressure variation and cavity opening at the bed up glacier from the riegel decoupling of the ice from the bed on the lowest parts of the riegel may have permitted the extrusion the return to more normal conditions in august appears to have been related to a decrease in ice flux over the riegel and a widening of the zone of decoupling

velocity discharge relationships derived from dye tracer experiments in glacial meltwaters implications for subglacial flow conditions repeated dye tracer tests were undertaken from individual moulins at haut glacier d arolla switzerland over a number of diurnal discharge cycles during the summers of 1989 1991 it was hoped to use the concepts of at a station hydraulic geometry to infer flow conditions in subglacial channels from the form of the velocity discharge relationships derived from these tests the results however displayed both clockwise and anticlockwise velocity discharge hysteresis in addition to the simple power function relationship assumed in the hydraulic geometry approach clockwise hysteresis seems to indicate that a moulin drains into a small tributary channel rather than directly into an arterial channel and that discharges in the two channels vary out of phase with each other anticlockwise hysteresis is accompanied by strong diurnal variations in the value of dispersivity derived from the dye breakthrough curve and is best explained by hydraulic damming of moulins or sub englacial passageways despite the complex velocity discharge relationships observed some indication of subglacial flow conditions may be obtained if tributary channels comprise only a small fraction of the drainage path and power function velocity discharge relationships are derived from dye injections conducted during periods when the supraglacial discharge entering the moulin and the bulk discharge vary in phase analyses based on this premise suggest that both open and closed channel flow occur beneath haut glacier d arolla and that flow conditions are highly variable at and between sites

bipolar changes in atmospheric circulation during the little ice age annually dated ice cores from siple dome west antarctica and central greenland indicate that meridional atmospheric circulation intensity increased in the polar south pacific and north atlantic at the beginning 1400 a d of the most recent holocene rapid climate change event the little ice age lia as deduced from chemical concentrations at these core sites the lia was characterized by substantial meridional circulation strength variability and this variability persists today despite strong evidence for an end to lia cooling thus increased late 20th century storm variability may be in part a result of the continuation of these climatic fluctuations

basal mechanics of ice stream b west antarctica 2 undrained plastic bed model based on the results of our studies of the physical conditions beneath ice stream b we formulate a new analytical ice stream model the undrained plastic bed model henceforth the upb model mathematically the upb model is represented by a non linear system of four coupled equations which express the relationships among ice sliding velocity till strength water storage in till and basal melt rate we examine this system of equations for conditions of ice stream stability over short timescales that permit holding ice stream geometry constant less than hundreds of years temporal variability is introduced into the upb model only by the direct dependence of till void ratio changes e t on the basal melting rate m r since till strength b e and ice stream velocity u b b change as long as till void ratio varies the first condition for ice stream stability is that of constant till water storage 0 the second condition for ice stream stability arises from the feedback between ice stream velocity till strength and the basal melting rate which depends on shear heating m r u b b this is the weak till condition which requires that in a steady state till strength is a small fraction of the gravitational driving stress b n 1 1 d the salient feature of the upb model is its ability to produce two thermo mechanically controlled equilibrium states one with a strong bed and slow ice velocities ice sheet mode and one with a weak bed and fast ice velocities ice stream mode this bimodality of basal conditions is consistent with the available observations of subglacial conditions beneath slow and fast moving ice in west antarctica basal conditions that do not correspond to these two steady states may occur transiently during switches between the two stable modes the upb model demonstrates that ice streams may be prone to thermally triggered instabilities during which small perturbations in the basal thermal energy balance grow leading to generation or elimination of the basal conditions which cause ice streaming

calibration of the speleothem delta function an absolute temperature record for the holocene in northern norway the speleothem delta function sdf provides a new transfer function between the d18o signal of speleothem calcite and surface ground temperature the function is based on physical principles relating d18o of the calcite to thermodynamic fractionation and to the dripwater function which in turn relates d18o of dripwaters to that of the local precipitation and thus to the modification of source water in relationship to the geographical position of the site the sdf must be calibrated against at least two reliable and well dated palaeotemperature points the end product is a reconstruction of absolute cave and surface temperatures the technique is tested using a holocene speleothem from north norway sg93 dated by 12 tims u th dates the reconstructed temperature curve is presented and compared with the gisp2 ice core record and with the historic record in both cases the correlation with sg93 is impressive indicating the validity of the technique

on the formation of the tunnel valleys of the southern laurentide ice sheet abstract catastrophic releases of meltwater produced by basal melting and stored for decades in subglacial reservoirs at high pressure may have been responsible for eroding the broad deep tunnel valleys that are common along the margins of some lobes of the southern laurentide ice sheet we surmise that these releases began when the high water pressure was transmitted to the margin through the substrate the water pressure in the substrate at the margin would then have been significantly above the overburden pressure leading to sapping failure headward erosion of a conduit in the substrate piping could then tap the stored water resulting in the outburst in some situations development of a siphon may have lowered the reservoir below its overflow level thus tapping additional water following the flood the seal could have reformed and the reservoir refilled setting up conditions for another outburst order of magnitude calculations suggest that once emptied a subglacial reservoir could refill in a matter of decades the amount of water released during several outbursts appears to be sufficient to erode a tunnel valley we think that tunnel valleys are most likely to have formed in this way where and when the glacier margin was frozen to the bed and permafrost extended from the glacier forefield several kilometers back under the glacier as reservoirs would then have been larger and more common and the seal more robust and more likely to reform after an outburst

the concept of cryo conditioning in landscape evolution recent accounts suggest that periglacial processes are unimportant for large scale landscape evolution and that true large scale periglacial landscapes are rare or non existent the lack of a large scale topographical fingerprint due to periglacial processes may be considered of little relevance as linear process landscape development relationships rarely can be substantiated instead periglacial landscapes may be classified in terms of specific landform associations we propose cryo conditioning defined as the interaction of cryotic surface and subsurface thermal regimes and geomorphic processes as an overarching concept linking landform and landscape evolution in cold regions by focusing on the controls on processes this concept circumvents scaling problems in interpreting long term landscape evolution derived from short term processes it also contributes to an unambiguous conceptualization of periglacial geomorphology we propose that the development of several key elements in the norwegian geomorphic landscape can be explained in terms of cryo conditioning

application of inventory data for estimating characteristics of and regional climate change effects on mountain glaciers a pilot study with the european alps a parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate change effects on mountain glaciers for past and potential climate scenarios glacier changes for assumed mass balance changes are calculated as step functions between steady state conditions for time intervals that approximately correspond to the characteristic dynamic response time a few decades of the glaciers in order to test the procedure a pilot study was carried out in the european alps where detailed glacier inventories had been compiled around the mid 1970s total glacier volume in the alps is estimated at about 130 km3 for the mid 1970s strongly negative mass balances are likely to have caused a loss of about 10 20 of this total volume during the decade 1980 90 backward calculation of glacier length changes using a mean annual mass balance of 0 25m w e a 1 since the end of the little ice age around 1850 ad gives considerable scatter but satisfactory overall results as compared with long term observations the total loss of alpine surface ice mass since 1850 can be estimated at about half the original value an acceleration of this development with annual mass losses of around 1 m a 1 or more as anticipated from ipcc scenario a for the coming century could eliminate major parts of the presently existing alpine ice volume within decades

a continental hydrological assessment of a new grid based digital elevation model of australia a rectangular grid digital elevation model dem for australia with a horizontal resolution of 1 40 degree of latitude and longitude approximately 2 5 km has recently been calculated from continent wide coverages of point elevation and stream line data using an elevation gridding technique which incorporates a drainage enforcement algorithm an automated drainage basin analysis of this dem is in close agreement with existing basin analyses both for the better surveyed coastal areas with well defined relief and for large areas of low relief that make up much of the interior lake eyre basin and the murray darling basin the analysis of the arid western plateau region differs from the currently accepted analysis but is in broad agreement with a previous analysis of palaeodrainage systems based on topographic and geological information the drainage analyses is used to calculate cumulative distributions of spatially distributed hydrologically significant terrain parameters for the murray darling and derwent river basins the adequacy of the resolution of the dem for continental hydrological analyses is assessed by comparing drainage basin analyses and cumulative distributions of terrain parameters at resolutions of 1 40th and 1 20th degree of latitude and longitude

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

evidence from northwest european bogs shows little ice age climatic changes driven by variations in solar activity fluctuations in holocene atmospheric radiocarbon concentrations have been shown to be due to variations in solar activity analyses of both 10 be and 14 c nuclides cone rm that production ratechanges during

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

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

is the longitudinal profile of storglaciaren northern sweden in balance with the present climate the main perturbation in the mass balance of storglaciaren during the twentieth century was caused by a sudden 1 c increase in the summer mean temperature around 1910 later perturbations of the climate have been of minor importance in relation to the mass balance annual field surveys suggest that the mass budget on storglaciaren has been in near balance for the last 15 years because of this major step like change we can establish the validity of theoretical models giving response times for storglaciaren of the order of 50 years according to these models storglaciaren could by now have reached a profile in balance with the present climate to study this problem the emergence velocity was calculated and compared with the net balance the result shows that the emergence velocity either balances or exceeds the net balance for the entire tongue except for the lowermost part where it decreases to about half of the net balance a slight further recession of the front position would thus be expected with today s climate calculated balance velocities also suggest that most of the present profile is close to a steady state profile if the mean annual sliding velocity is about 50 of the surface velocity lower sliding velocities would imply a thickening

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

feedbacks between coupled subglacial hydrology and glacier dynamics on most glaciers and ice sheet outlets the majority of motion is due to basal slip a combination of basal sliding and bed deformation the importance of basal water in controlling sliding is well established with increased sliding generally related to high basal water pressure but the details of the interactions between the ice and water systems has not received much study when there is coupling between the systems here we use coupled subglacial hydrology and ice dynamics models within the community ice sheet model to investigate feedbacks between the ice and water systems the dominant feedback we find is negative sliding over bedrock bumps opens additional cavity space which lowers water pressure and in turn sliding we also find two small positive feedbacks basal melt increases through frictional heat during sliding which raises water pressure and strain softening of basal ice during localized speedup causes cavities to close more quickly and maintain higher water pressures our coupled modeling demonstrates that a sustained input of surface water to a distributed drainage system can lead to a speedup event that decays even in the absence of channelization due to increased capacity of the system through opening of cavities which is enhanced through the sliding opening feedback we find that the negative feedback resulting from sliding opening is robust across a wide range of parameter values however our modeling also argues that subglacial channelization is required to terminate speedup events over timescales that are commensurate with observations of late summer slowdown on mountain glaciers

esker characteristics in terms of glacier physics katahdin esker system maine the characteristics of large subglacially formed eskers such as the katahdin system are closely related to two special peculiarities of water filled tunnels along the beds of ice sheets 1 the water pressure approximates the weight of the overlying ice and 2 in tunnels that descend and those that ascend less steeply than 1 7 times the ice surface gradient the walls melt producing a sharply arched tunnel cross section whereas in those that ascend more steeply they freeze producing a wide low one the first peculiarity primarily governs the paths of these eskers it causes the tunnels to follow the paths ordinary rivers would follow were the land tipped downglacier 11 times the local ice surface gradient the paths therefore trend in the general direction of the former ice flow but tend to deviate so as to follow valleys and to cross divides at the lowest passes as observed ice surface gradients calculated from path deviations at two localities on the katahdin esker system indicate relatively thin sluggish ice the surface of which lay 200 m below the summit of mount katahdin in agreement with independent geologic evidence the second peculiarity primarily governs the form composition and structure of these eskers strong melting causes a large inflow of basal ice and entrained debris to the tunnel and produces sharp crested eskers of poorly sorted poorly bedded sand gravel and boulders with lithologies like the adjacent till whereas weaker melting produces multiple crested ones of similar composition freezing precludes inflow and produces broad crested eskers of fairly well sorted well bedded more water worn coarse sand with few large clasts ice surface gradients calculated from transitions from the multiple crested type to small areas of broad crested type on the katahdin system agree closely with those computed from the paths at nearby localities an anomalously low gradient calculated from a transition to an area of broad crested type approximately twice as wide and long as the probable ice depth apparently confirms that as expected the basal ice was supported by water pressure over most if not all of the width of the esker

tv video observations of bed and basal sliding on storglaciaren sweden four boreholes in storglaciaren a small valley glacier in northernsweden were inspected with a video camera in two of the boreholes the apparentglacier bed was filmed in one borehole the bed was found to be composed of softsediment but in the other it consisted of bedrock in the latter the camera moved5 6 mm relative to the bed during an 80 min period the recorded camera movementshowed a background motion which is in the expected range of basal sliding superimposed on the background motion a jerky motion of a high speed spike wasfound the jerky motion is interpreted as a stress release induced by local topographyat the ice bed interface

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

a new approach to calculating holocene winter precipitation by combining glacier equilibrium line altitudes and pine tree limits a case stud from hardangerjokulen central southern norway at hardangerjokulen central southern norway detailed knowledge of the number age and magnitude of holocene glacier fluctuations is used to reconstruct variations in equilibrium line altitude ela for the last 10 000 years present and past elas are based on an accumulation area ratio aar of 0 7 and are adjusted for land uplift a synchronous relationship between advanced glacier positions and the highest pine tree limits pinus sylvestris l is demonstrated for the early to mid holocene in southern scandinavia which indicates that warm summers were compensated for by high winter precipitation based on pine tree limit fluctuations as a measure of mean ablation season temperature holocene variations in winter precipitation at hardangerjokulen have been calculated by substitution in the close exponential relationship between mean ablation season temperature and winter precipitation at the ela of norwegian glaciers setting the winter precipitation during the period ad 1961 1990 at 100 mean values

waterways ice permeability at depth and water pressures at glacier d argentiere french alps pour eclaircir les changements survenus a la prise d eau sous glaciaire du glacier d argentiere une etude approfondie a ete realisee en 1979 80 avec 31 forages et un carottage jusqu au fond 240m juste en amont de la prise dans une zone surcreusee on observe que la glace en dessous d environ 100 m de profondeur est legerement permeable on a mesure la pression interstitielle de l eau dans la glace profonde le gradient piezometrique entre les trous de forage et le dephasage entre les fluctuations du niveau d eau qui augmente lorsqu on s eloigne de la rive droite il n y a pas de torrent sous glaciaire au fond du surcreusement sauf a son extremite amont la plupart de l eau de fonte doit s ecouler entre glace et rocher le long de la rive droite sa surface libre s elevant d environ 150 m au moment de l engorgement de juin on n a pas trouve de correlation nette entre la pression de l eau interstitielle profonde et la temperature de l air ou le debit a la prise sous glaciaire en aval

using concurrent dna tracer injections to infer glacial flow pathways author s dahlke he williamson ag georgakakos c leung s sharma an lyon sw walter mt abstract 2015 john wiley a sons ltd catchment hydrology has become replete with flow pathway characterizations obtained via combinations of physical hydrologic measurements e g streamflow hydrographs and natural tracer signals e g stable water isotopes and geochemistry in this study we explored how our understanding of hydrologic flow pathways can be improved and expanded in both space and time by the simultaneous application of engineered synthetic dna tracers in this study we compared the advective dispersive transport properties and mass recovery rates of two types of synthetic dna tracers one consisting of synthetic dna strands encapsulated into biodegradable microspheres and another consisting of free dna i e not encapsulated the dna tracers were also compared with a conservative fluorescent dye all tracers were injected into a small 3 2 km2 valley glacier storglaciaren in northern sweden seven of the nine dna tracers showed clear recovery during the sampling period and similar peak arrival times and dispersion coefficients as the conservative fluorescent dye however recovered dna tracer mass ranged only from 1 to 66 while recovered fluorescent dye mass was 99 resulting from the cold and opaque subglacial environment provided by the glacier mass loss associated with microbial activity and photochemical degradation of the dna is likely negligible leaving sorption of dna tracers onto suspended particles and loss of microtracer particles to sediment storage as probable explanations despite the difference in mass recovery the advection and dispersion information derived from the dna tracer breakthrough curves provided spatially explicit information that allowed inferring a theoretical model of the flow pathways that water takes through the glacier

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

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

the briksdalsbre event a winter precipitation induced decadal scale glacial advance in southern norway in the ad 1990s and its implications in the ad 1990s maritime glaciers in scandinavia started to advance as a response to positive net mass balance in the preceding years invoking annual advance rates in the order of 50 60 m and a total frontal advance of 285 m at briksdalsbreen in less than a decade records from six south norwegian glaciers with continuous annual front measurements are used to evaluate the magnitude duration climatic causes and frontal time lags involved in this mass balance perturbation and the following frontal response of glaciers in southern norway a climate index based on meteorological data from bergen unequivocally demonstrates that the main cause for the large glacier advances in scandinavia in the 1990s was high winter precipitation linked to positive nao index in the winters of 1988 1989 1989 1990 1992 1993 1994 1995 1997 1998 and 1999 2000 less positive or negative glacier mass balance years were 1990 1991 1993 1994 1995 1997 and 1998 1999 between 1996 1997 and 2009 briksdalsbreen retreated

holocene glacier history of bjornbreen and climatic reconstruction in central jotunheimen norway based on proximal glaciofluvial stream bank mires abstract holocene variations of bjornbreen smorstabbtinden massif west central jotunheimen are reconstructed from the lithostratigraphy of two alpine stream bank mires flooded episodically by meltwater the approach uses multiple sedimentological indicators weight loss on ignition mean grain size grain size fractions bulk density moisture content and magnetic susceptibility an a priori model of overbank deposition of suspended glaciofluvial sediments a detailed chronology based on 56 radiocarbon dates and a little ice age sedimentological analogue rapid late preboreal deglaciation was indicated by immigration of betula pubescens by 9700 cal bp an interval of at least 3000 years in the early holocene when glaciers were absent was interrupted by two abrupt episodes of glacier expansion around the time of the finse event the first at ca 8270 7900 cal bp bjornbreen i event and the second at ca 7770 7540 cal bp bjornbreen ii event neoglaciation began shortly before ca 5730 cal bp with gradual build up to the maximum of the bjornbreen iii event at ca 4420 cal bp later maxima occurred at ca 2750 cal bp bjornbreen iv event and at 1300 1260 1060 and 790 cal bp all within the bjornbreen v event glaciers were smaller than today and possibly melted away on several occasions in the late holocene ca 3950 1410 and 750 cal bp minor maxima also occurred at ca 660 and 540 cal bp within the late mediaeval warm period and the early little ice age respectively the little ice age maximum was dated to 213 25 bp ca 205 cal bp the relative magnitudes of the main glacier maxima were determined erdalen event little ice age event bjornbreen vi bjornbreen i finse event bjornbreen ii bjornbreen v bjornbreen iv bjornbreen iii these episodic events of varying magnitude and abruptness were used in conjunction with an independent summer temperature proxy to reconstruct variations in equilibrium line altitude ela and a holocene record of winter precipitation since the preboreal ela varied within a range of about 390 m and winter precipitation ranged between 40 and 160 of modern values winter precipitation variations appear to have been the main cause of these century to millennial scale holocene glacier variations

current transition from glacial to periglacial processes in the dolomites south eastern alps abstract a close relationship between glacial and periglacial landforms is frequently observed in alpine environments where a transition from glacial to periglacial processes often took place after the end of the little ice age lia understanding the origin of these landforms is challenging and assessing the current spatial domain of glacial and periglacial processes may be a difficult task in high relief areas where thick and widespread debris cover often characterize rapidly decaying glaciers here we present a comprehensive study of a composite landform located in the dolomites south eastern alps combining geomorphological geophysical and topographic surveys with ground surface temperature measurements results indicate that a debris covered glacier persists in the upper part rather large compared to the lia extent but currently inactive and rapidly losing mass an active rock glacier exists in the lower part surrounded by discontinuous permafrost a frozen body about 10 m thick was detected in the rock glacier and geomorphological evidence suggests that this ice mass is completely detached from the debris covered glacier our findings suggest that the lower part of the composite landform is probably a remnant of the ancient glacier tongue and is currently evolving under periglacial conditions periglacial processes are therefore replacing glacial processes which dominated in this site during the lia

geomorphic implications of subglacial drainage configuration rates of basal sediment evacuation controlled by seasonal drainage system evolution abstract although basal sediment evacuation by subglacial meltwater is widely assumed to dominate the sediment budget of most temperate glaciers and ice caps its potential influence for glacial geomorphic processes and landforms has largely been overlooked in the glacial literature data collected at haut glacier d arolla switzerland during the 1998 ablation season are used to test theoretical predictions that subglacial drainage configuration should exert a primary control on rates of basal sediment evacuation by subglacial meltwater seasonal evolution of the subglacial drainage system enables observation of sediment evacuation from both distributed and channelised drainage systems daily suspended sediment load exhibits an extreme nonlinear increase with respect to discharge between winter and summer periods which correspond to periods of predominantly distributed and channelised subglacial drainage respectively these results suggest that subglacial drainage configuration should significantly impact upon a rates of subglacial erosion and debris production b the nature of debris transport and the proportion of sediment in glacial versus fluvioglacial transport pathways and c rates and styles of ice marginal sedimentation in contrast to their distributed counterparts channelised drainage configurations are predicted to encourage subglacial erosion through the removal of basal sediment from the ice bedrock interface and with the exception of supraglacial transport will discourage sediment transport by alternative glacial mechanisms direct sedimentation at the glacier margin may therefore be reduced resulting in smaller moraines despite an overall increase in sediment production an appreciation of the coupling between glacier hydrology and geomorphic processes suggests new frameworks for the understanding of rates and styles of glacial erosion sediment transfer and deposition and the complex geomorphology of ice marginal environments

short term velocity and water pressure variations down glacier from a riegel storglaciaren sweden during the 1991 94 summer field seasons time correlated measurements of water pressure and surface speed were made over and down glacier from a major riegel on storglaciaren sweden measurements were made at sub hourly time scales in order to discern details in the diurnal cycle large water input events typically associated with rain storms produced coherent lagged surface velocity responses that could be understood in terms of till deformation or decoupling and these have been discussed elsewhere the consequences of smaller diurnal water pressure events were more enigmatic in that acceleration of ice flow generally preceded the onset of the local water pressure rise from consideration of these data and other work done on the hydrology of storglaciaren we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel hence accelerations occur in response to increases in water pressure that occur up glacier and that precede local water pressure rises in addition following a period of large storm events surface speeds became more spatially coherent and were in phase with the diurnal ater pressure cycle this suggests that the large water pressure events lead to a spatially more homogeneous subglacial drainage system sliding laws need to take into accoun such temporal changes in spatial coherence of the subglacial drainage system

vertical extension of the subglacial drainage system into basal crevasses water plays a first order role in basal sliding of glaciers and ice sheets and is often a key constituent of accelerated glacier motion subglacial water is known to occupy systems of cavities and conduits at the interface between ice and the underlying bed surface depending upon the history of water input and the characteristics of the substrate full understanding of the extent and configuration of basal water is lacking however because direct observation is difficult this limits our ability to simulate ice dynamics and the subsequent impacts on sea level rise realistically here we show that the subglacial hydrological system can have a large volume of water occupying basal crevasses that extend upward from the bed into the overlying ice radar and seismic imaging combined with in situ borehole measurements collected on bench glacier alaska reveal numerous water filled basal crevasses with highly transmissive connections to the bed some crevasses extend many tens of metres above the bed and together they hold a volume of water equivalent to at least a decimetre layer covering the bed our results demonstrate that the basal hydrologic system can extend high into the overlying ice mass where basal crevasses increase water storage capacity and could potentially modulate basal water pressure because basal crevasses can form under commonly observed glaciological conditions our findings have implications for interpreting and modelling subglacial hydrologic processes and related sliding accelerations of glaciers and ice sheets

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

outburst flooding and the initiation of ice stream surges in response to climatic cooling a hypothesis abstract outburst flooding from subglacial reservoirs and associated surging of ice streams are caused by processes following climatic cooling that produce ice shelf grounding on proglacial sills trapping subglacial water according to an hypothesis presented here glaciers often advance into proglacial water bodies cooling may allow ice shelf formation and advance causing grounding on a proglacial sill trapping subglacial water ice shelf freeze on to the sill and development of a local reversal in ice air surface slope over the sill then are likely allowing ice thickening and water overpressurization if basal thawing then occurs as is likely an outburst flood and a surge may be triggered these processes may have been involved in heinrich events generation of antarctic subglacial lakes and meltwater scouring of some regions

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

cold temperate transition surface and permafrost base cts pb as an environmental axis in glacier permafrost relationship based on research carried out on the storglaciaren and its forefield northern sweden here we present empirical ground penetrating radar gpr and electroresistivity tomography data ert to verify the cold temperate transition surface permafrost base cts pb axis theoretical model the data were collected from storglaciaren in tarfala northern sweden and its forefield the gpr results show a material relation between the glacial ice and the sediments incorporated in the glacier and a geophysical relation between the cold ice and the temperate ice layers clearly identifying lateral glacier margins is difficult as periglacial and glacial environments frequently overlap in this case we identified areas showing permafrost aggradation already under the glacier particularly where the cts is replaced by the pb surface this structure appears as a result of the influence of a cold climate over both the glacial and periglacial environments the results show how these surfaces form a specific continuous environmental axis thus both glacial and periglacial areas can be treated uniformly as a specific continuum in the geophysical sense similarly other examples previously described also allow identifying a continuation of permafrost from the periglacial environment onto the glacial base in addition the ert results show the presence of double layered periglacial permafrost possibly suggesting a past climatic fluctuation in the study area

cosmogenic 10be and 26al exposure ages of tors and erratics cairngorm mountains scotland timescales for the development of a classic landscape of selective linear glacial erosion abstract the occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre quaternary landscapes beneath protective covers of non erosive dry based ice here we test for the preservation of pre quaternary landscapes with cosmogenic surface exposure dating of tors numerous granite tors are present on summit plateaus in the cairngorm mountains of scotland where they were covered by local ice caps many times during the pleistocene cosmogenic 10be and 26al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected many cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides as the surfaces have been subject to episodic burial by ice an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data exposure ages and weathering characteristics of tors are closely correlated glacially modified tors and boulder erratics with slightly weathered surfaces have 10be exposure ages of about 15 to 43 ka nuclide inheritance is present in many of these surfaces correction for inheritance indicates that the eastern cairngorms were deglaciated at 15 6 0 9 ka glacially modified tors with moderate to advanced weathering features have 10be exposure ages of 19 to 92 ka these surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine oxygen isotope stage 5 or earlier tors lacking evidence of glacial modification and exhibiting advanced weathering have 10be exposure ages between 52 and 297 ka nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events maximum erosion rates estimated from 10be range from 2 8 to 12 0 mm ka with an error weighted mean of 4 1 0 2 mm ka three of these surfaces yield model exposure plus burial ages of 295 71 84 520 141 178 and 626 85 102 ka a vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long term emergence rate of 31 2 mm ka these findings show that dry based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous too old exposure ages while many cairngorm tors have survived multiple glacial cycles rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre quaternary rock surfaces

structural analysis of hypocentral distribution of an earthquake sequence using anisotropic wavelets method and application 1 spatial organization of earthquake sequences is investigated to localize active rupture planes and to reconstruct the geometry of the inferred rupture zone we have developed a new approach the normalized optimized anisotropic wavelet coefficient noawc method to extract from a set of hypocenters the active ruptures planes our approach permits the detection of organized structures within a plane regardless of its size location shape anisotropy and orientation it includes the determination of a system of three perpendicular sections minimizing the effects of projections of the hypocenters and intrinsically accounts for uncertainty in the location of the seismic events the accuracy and the effectiveness of the noawc procedure are illustrated on both synthetic and real data an application to the m 5 1 arudy french pyrenees aftershock sequence shows how a combination of the possible mathematically reconstructed geometries can be combined with the available fault plane solutions and geomorphological markers to determine the active rupture planes and to propose and validate a local tectonic model this new multitool approach lends itself to quantitative and computer assisted analyses of large data sets

holocene glacier fluctuations of flatebreen and winter precipitation changes in the jostedalsbreen region western norvay based on glaciolacustrine sediment records the history of holocene glacier variations of flatebreen an independent glacier close to the sw part of the jostedalsbreen ice cap has been reconstructed from lacustrine sediments in the proglacial lake jarbuvatnet the sedimentary succession shows evidence of three maini episodes of holocene glacier expansion the first is recorded in the basal part of the core up to 370 cm according to the age depth relationship in the sediment core based on 12 ams radiocarbon dates this glacier expansion episode terminated about 10200 cal yr bp the second major glacier phase lasted from 8400 to 8100 cal yr bp while the third was initiated around 4000 cal yr bp and has continued up to the present at 43 cm in the core the medium silt content increases significantly accompanied by a minor increase in the sand content this textural change is interpreted as the first time that the tenninus of flatebreen extended inlto an upstream lake at 1083 m a s l the age model suggests that this event took place around

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