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

double averaging concept for rough bed open channel and overland flows theoretical background the goal of this paper is to discuss the spatial averaging concept in environmental hydraulics and develop it further by considering transport equations for fluid momentum passive substances and suspended sediments the averaging theorems the double averaged in time and in space fluid momentum equation and advection diffusion equations for a passive substance and suspended sediments are introduced and their limitations and applications for modeling rough bed flows experimental design and data interpretation are discussed the suggested equations differ from those considered in terrestrial canopy aerodynamics and porous media hydrodynamics by accounting for roughness mobility change in roughness density in space and time and particle settling effects for the case of suspended sediments we show that the form of the double averaged equations may depend on the type of decomposition of flow variables and that this difference may have important implications for modeling we also show that the suggested methodology offers better definitions for hydraulic characteristics variables and parameters such as flow uniformity flow two dimensionality and bed shear stress

coastal and near shore changes correlated with die back in eel grass zostera marina l abstract the die back of eel grass zostera marina l is found to have played an important role with regard to near shore sedimentation and coastal changes in a natural harbour at kyholm denmark a hiatus is found between silty sediments that date from about 4000 bc and overlying modern sandy sediments it is suggested that this is a consequence of the die back of eel grass in the nineteen thirties resulting in mobilisation and disturbance of nearshore sediments and the shoreward movement of mobilised sandy material into the harbour the coastal morphology of kyholm was relatively stable from 1802 to 1933 but between 1933 and 1978 there have been two periods of drastic progradation correlated with die back of eel grass

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

the use of borehole video in investigating the hydrology of a temperate glacier a geovision micro colour video camera was used to investigate the internal structure of 11 boreholes at haut glacier d arolla switzerland the boreholes were distributed across a half section of the glacier with closest spacing towards the glacier margin the boreholes were used to investigate the hydrology of the glacier through automatic monitoring of borehole water level and electrical conductivity ec at the glacier bed ec profiling was undertaken in several boreholes to determine the existence of water quality stratification temporal variations in ec stratification were used to infer borehole water sources and patterns of water circulation borehole video was used to confirm the conclusions made from these indirect sources of evidence and to provide an independent source of information on the structure and hydrology of this temperate valley glacier the video showed variations in water turbidity englacial channels and voids conditions at the glacier bed and down borehole changes in ice structure based on the video observations englacial channels accounted for approximately 0 1 of the vertical ice thickness and englacial voids for approximately 0 4 overall the video images provided useful qualitative and semi quantitative data that reinforce interpretations of a range of physical and chemical parameters measured in boreholes 1997 by john wiley sons ltd

extension tectonics in the wessex basin southern england the permian to cretaceous tectonic evolution of the wessex basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere the gross morphologies of its constituent structures were governed by the location of variscan thrust and wrench faults in the upper and middle crust which suffered extensional reactivation in tensional stress fields oriented approximately nw se several episodes of crustal extension can be resolved in early permian early triassic early jurassic and late jurassic early cretaceous times these were characterized by the rapid subsidence of fault bounded basins and commonly by erosion of adjacent upfaulted blocks superimposed upon the fault controlled subsidence dominant during periods of fault quiescence and becoming increasingly important with time a component of regional subsidence is considered to have a thermal origin this suggests that crustal extension was accompanied by some form of not necessarily uniform lithospheric thinning subsidence analyses assuming local airey isostasy give cumulative crustal extension factors of 20 28 beneath the grabens a more reasonable assumption of regional airey compensation indicates basinwide crustal extension of 13 17 which is consistent with birps offshore deep seismic reflection data

modeling the diurnal variation of tracer transit velocity through a subglacial channel 1 tracer injections into a moulin connecting to a subglacial channel at unteraargletscher were repeated at intervals of about two hours over two diurnal discharge cycles in august and september 2000 the pronounced hysteresis in the relationships between tracer transit velocity and proglacial discharge may be explained by adjustments of the channel cross section in response to discharge variations or alternatively by modulation of inflow from the tributary moulin into a main subglacial channel to test these hypotheses we employ a physically based time dependent model of channelized subglacial drainage in a series of numerical experiments we explore the general characteristics of each mechanism before the model is applied to diurnal discharge variations measured during the tracer tests at unteraargletscher we found that the ability of a rothlisberger channel to adjust its size to the prevailing hydraulic conditions can contribute to the hysteresis in the velocity discharge relationships however using plausible parameter values r channel hydraulics alone is not satisfactory in reproducing the magnitude of observed transit velocities the model further confirms that retardation of the tracer in the tributary moulin due to inflow modulation has major effects on transit velocities both in magnitude and timing with appropriate assumptions on channel sinuosity and moulin size a combination of both mechanisms can be found that is capable of reproducing the observed transit velocities

diurnal variability of subglacial drainage conditions as revealed by tracer experiments 1 the morphology of the drainage system of unteraargletscher switzerland and the diurnal variability of drainage conditions were investigated by conducting a series of tracer tests over a number of discharge cycles during the ablation season 2000 dye injections into a moulin were repeated at intervals of a few hours and were accompanied by simultaneous measurements of discharge of supraglacial meltwater draining into the moulin and bulk runoff in the proglacial stream fast transit velocities in conjunction with low dispersion values suggest that the tracer was routed through a hydraulically efficient channelized drainage system however detailed analyses reveal a large diurnal variability in terms of transit velocity and dispersion coefficient this finding underlines the difficulty of detecting a possible drainage system evolution based on single tracer tests conducted at coarse temporal intervals furthermore the obtained velocity discharge relationships display pronounced hysteresis we suggest that the evolution of the cross sectional area of an ice walled conduit and the modulation of inflow at the junction of a tributary moulin to a main subglacial channel are responsible for the observed behavior

discharges of turbid water during mini surges of variegated glacier alaska u s a discharges of water sediment and dissolved impurities from variegated glacier ala ska were monitored in the early summers of 1980 and 1981 during the occurrence of mini surg es sea sonal trends weat her related eve nts and diurnal variat ions similar to behavior of other temperat e gl acier streams were found the prin cipal effect in the stream associated with mini surge occurrence was a brief discharge of extremely turbi d water the turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini surge at a time and locat ion on the upper glacier known from oth er meas ure ments the mean water velocity in the hydraulic system over the int erven ing distance is thereby determined 0 3 m s i the mean water velocity together with the water discharge 16 m3 s 1 at the terminus places con straints on the distribution of water velocity u and total cros s sectional area at of the flow paths along the gl acier base this leads to the con clusion that within the zone of mini surge occurrence in its unpe rturbed state u is about 0 1 m s 1 or possibly less at is about 10 2 m2 or possibly more and it must be divided into a very large number of small passag eways be blocked by constrict ions or both the total water cro ss se ction corresponds to a layer 0 1 2 m thick when spr ead unifo rmly over the glacier width the water velocity is clos e to or less than the propa gation velo city of the mini s urges bet ween the zone affected by mini surges and the stream a dyna mically less active lower section of the glacier is proba bly underlain by a small number of conduits in which the water velocity may be very high 2 m s i water di scharge follo wing the mini surges puts an upper limit on water storage changes ass ociated with the anomalous ice motion

comparing different methods of bed shear stress estimates in simple and complex flow fields bed shear stress is a fundamental variable in river studies to link ow conditions to sediment transport it is however dif cult to estimate this variable accurately particularly in complex ow elds this study compares shear stress estimated from the log pro le drag reynolds and turbulent kinetic energy tke approaches in a laboratory ume in a simple boundary layer over plexiglas and over sand and in a complex ow eld around de ectors results show that in a simple boundary layer the log pro le estimate is always the highest over plexiglas the tke estimate was the second largest with a value 30 per cent less than the log estimate however over sand the tke estimate did not show the expected increase in shear stress in a simple boundary layer the reynolds shear stress seems the most appropriate method particularly the extrapolated value at the bed obtained from a turbulent pro le in a complex ow eld around de ectors the tke method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent uctuations close to the de ectors it is suggested that when single point measurements are used to estimate shear stress the instrument should be positioned close to 0 1 of the ow depth which corresponds to the peak value height in pro les of reynolds and tke shear stress copyright 2004 john wiley sons ltd

palaeoenvironmental significance of storm coquinas in a lower cretaceous coastal lagoonal succession vectis formation isle of wight southern england thin bioclastic limestone beds coquinas in the vectis formation wealden group lower cretaceous of the isle of wight southern england exhibit a range of biofabrics and internal stratigraphies these features are attributed to both simple and complex storm deposition of allochthonous biogenic and siliciclastic materials in coastal lagoons and on adjacent mudflats these modes of deposition facilitated preservation of dinosaur trackways desiccation cracks shallow tier trace fossils and in situ bivalve colonies through rapid burial the coquinas thus preserve a record of surficial muds commonly lost through reworking the principal components of the coquinas comprise dispersed elements from within the argillaceous background facies some of these beds are laterally traceable for up to 27 km providing the foundations for a high resolution event stratigraphic framework

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

elucidating changes in the degree of tracer dispersion in a subglacial channel tracer injections into a subglacial channel at unteraargletscher switzer land were repeated at intervals of about 2 hours over two diurnal discharge cycles in august and september 2000 records of dye concentration reveal a pronounced hysteresis in the velocity dispersion relationship thereby indicating alterations in the drainage system theoretical considerations for ro thlisberger channels suggest an evolution of the conduit cross section in response to a diurnally varying discharge we studied the relation between conduit cross section and tracer dispersion with numerical tracerexperiments thevelocity fieldforsteady flow throughagivenconduitgeometry is calculated using a commercial flow solver tracer transport is represented by a scalar volume which is advected by the velocity field experiments were conducted for several scenarios by varying flow velocity conduit geometry and conduit roughness results show only a weak dependence of dispersion on conduit size in contrast changes in roughness of the conduit walls reveal a strong effect on tracer dispersion therefore to explain the observed hysteresis in the velocity dispersion relationship we suggest that the evolution of a subglacial flow path might involve changes in roughness

large woody debris structures for sand bed channels described is a method for channel erosion control and habitat rehabilitation featuring intermittent placement of structures made of large woody debris this method is expressly tailored to address severe problems typical of incised channels with little sediment coarser than sand in these types of environments buoyancy forces are typically more important factors in woody debris stability than fluid drag buoyant forces are counteracted by the weight of the structure earth anchors and sediment deposits design concepts were tested in a demonstration project constructed along 2 km of channel draining a 37 km watershed large woody debris structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention construction costs per unit channel length were 23 58 of costs for recent stone bank stabilization projects within the same region during the second year following construction 31 of the structures failed during high flows probably due to inadequate anchoring

spatially averaged flows over mobile rough beds definitions averaging theorems and conservation equations abstractthis paper reports the double averaged in space and in time hydrodynamic equations for mobile boundary conditions that are derived based on the refined double averaging theorems modified reynolds decomposition and improved definitions of the spatial and time bed porosities the obtained double averaged conservation equations provide a mathematical framework for studying mobile boundary flows such as gravel bed rivers during flood events or flows over vegetated beds these equations will help in designing measurement campaigns for obtaining mobile bed data and their interpretation and parameterization eventually leading to improved and more robust predictive models

lagoonal sedimentation and fluctuating salinities in the vectis formation wealden group lower cretaceous of the isle of wight southern england abstract sedimentation in the shepherd s chine member of the vectis formation is characterised by a cyclicity of four principal facies on which a strong asymmetry has been imprinted by erosional events the four lithofacies are 1 very fine to fine sandstones 2 heterolithic sand silt and mudstones 3 parallel laminated pinstripe mudstones and 4 black mudstones the biota principally associated with lithofacies 2 and 3 as shelly partings and coquinas can be grouped into five molluscan associations which range from freshwater to quasi marine these associations are poorly correlated with the lithofacies but fluctuate within and between cycles salinity and storm frequency increase towards the top of the formation heralding the main marine aptian transgression lithofacies and biotas indicate deposition in a lagoon that was shallow and temporarily emergent the cyclicity is thought to represent the more distal phases of the advance and retreat of deltaic sand bodies derived from a westerly direction into the lagoon major storm events broke the symmetry of the cycles a deltaic facies represented by the barnes high sandstone member is thought to be laterally linked reworked deltaic sandstone lobes

geometry and flow conditions of subglacial water at south cascade glacier washington state u s a an analysis of tracer injections tracers were injected into south cascade glacier to determine the flow condition and geometry of the subglacial water system results indicate that two distincts drainage basins on the glacier feed the two main streams flowing from the glacier in the largest basin two parallel drainage networks exist one englacial and the other subglacial

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

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

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

prediction of mean turbulent flow velocity in a permeable walled pipe abstract determining the characteristics of pipe flow and the effect of friction resistance is relevant to a variety of applications in hydraulic and hydrological engineering such as flood control river restoration and ground runoff prediction in the nikuradse s experiments the relative roughness and the bulk reynolds number are used to scale the darcy friction factor thereby determining the mean velocity recent observations using permeable walled pipes however indicate that the friction factor can significantly deviate from the results obtained in nikuradse s approach here we propose a concise model to estimate the mean velocity of the pipe flow over permeable walls the model is formulated using a data driven approach based on the analytical solution of the mean velocity and the similarity analysis dimension conservation of the two extreme cases impermeable and porous pipe flow we show that the proposed approach can derive a physically meaningful formula for the mean velocity furthermore we propose a simple momentum transfer model which confirms the findings from the data driven approach the momentum transfer model indicates that the friction factor can be scaled with two different relative hydraulics radius scales which are intrinsically determined by two different eddy sizes lastly the present approach is examined by comparing it with another approximate formula and the limited experimental data in the literature

dye tracing a jokulhlaup i subglacial water transit speed and water storage mechanism we present results of an investigation of two j okulhlaups glacial lake outburst floods at gornergletscher switzerland using dye tracer experiments and complementary hydrological measurements repeated dye injections into moulins showed that tracer transit speeds were larger after the lake had emptied but when proglacial discharge was still high than during the main phase of the j okulhlaup this counter intuitive finding was modelled by tracer retardation inside the injection moulin this model together with an estimate of the maximum time the tracer takes to transit the injection moulin allows us to calculate bounds on the transit speed in the main drainage channel where the lake water flows these results indicate that the main drainage channel transit speeds are indeed highest during the peak of the flood moreover it is known from a previous study that water amounting to half of the lake volume is temporarily stored within the glacier during a gornergletscher j okulhlaup our observations suggest that this process occurred via lateral spreading of water at the glacier bed

evidence for excess pore water pressure generated in subglacial sediment implications for clast ploughing 1 pore water pressure in front of an object pulled through subglacial sediment and water pressure at the base of a borehole were simultaneously recorded at unteraargletscher switzerland to investigate the generation of excess pore pressures downglacier from ploughing clasts analysis of the strongly correlated pressure records revealed that the amplitude of the pore pressure fluctuations was larger than that of the corresponding borehole pressure fluctuations guided by high temporal resolution measurements of glacier surface motion from a different year this finding suggests that temporal changes in glacier speed lead to changes in the degree of excess pore pressure in front of the ploughing object the generation of excess pore water pressure has the potential to weaken the sediment downglacier from ploughing clasts instead of these clasts providing the roughness at the ice bed interface to resist glacier motion the ploughing process may in fact help to decouple the ice from the bed reducing basal resistance

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

on the formation of the tunnel valleys of the superior lobe central minnesota abstract when considering the formation of tunnel valleys most researchers have appealed to basal melting as the primary source of water erosion of the tunnel valleys can then be accomplished by steady state drainage over a long period or by storage and subsequent catastrophic release however field relationships in a large system of tunnel valleys formed by the superior lobe in central minnesota indicate that another source of water must be considered the minnesota tunnel valleys are composed of individual segments 10 20 km long and the segments commonly terminate in subaerial outwash fans at recessional ice margin positions eskers associated with the tunnel valleys are also composed of short segments frequently beginning at moulin kames and terminating at the head of outwash fans the dominant source of the water responsible for tunnel valley formation was seasonal meltwater from the glacier surface that reached the bed through moulins and crevasses the apparent continuity of the valleys resulted from the headward development of the englacial drainage system during ice retreat

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

depositional events and their records an introduction abstract event deposits of some lateral extent as defined here occur almost in all types of sedimentary basins the reflect either local intra basinal processes or they are associated with regional or global mechanisms some types of event beds such as sediment gravity flows sandy and muddy turbidites are common and usually well preserved they make up large proportions of basin fills whereas others e g tsunami deposits and in situ earthquake structures appear to be less frequent or rare in the geological record volume frequency and facies of event deposits are controlled by several processes pre event sediment accumulation triggering and transport mechanisms and mode of final deposition

estimating local bed shear stress from velocity observations replicate velocity observations using conventional equipment under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements the bed shear velocity u can be estimated within 3 using the depth averaged velocity in the vertically averaged logarithmic velocity profile to be accurate this method is limited to relatively simple flow geometries which may be expected to have the appropriate velocity structure estimates of u made using a single near bed velocity observation are less precise by a factor of 3 because of the larger uncertainty associated with a single observation accuracy of this method requires appropriate flow conditions only near the bed so it may be applied in a wider range of flow conditions including spatially variable flow estimates of u from the slope of the near bed velocity profile are the least precise and require the most restrictive flow conditions for accuracy but offer the advantage that they may be made without independent knowledge of the bed roughness different methods for estimating roe should be useful in judging the precision of estimates made under similar conditions these estimates of precision together with considerations of convenience and model accuracy provide the basis for select ing the most appropriate or advantageous method for different conditions and purposes

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

sediment retention by a mediterranean posidonia oceanica meadow the balance between deposition and resuspension the role of posidonia oceanica in promoting sediment stability and accretion was studied in a 15 m deep meadow at fanals point nw mediterranean spain by comparing particle deposition within the meadow and adjacent bare sediment small sediment traps were used to measure deposition within and above the meadow and over bare sand a model based on measurements of particle deposition at increasing distances from the bottom was used to partition the total depositional flux between primary sediment particles deposited for the first time at the measuring site and resuspended deposition sediment particles that have been previously deposited at the measuring site measurements were conducted monthly over a year to establish the magnitude and seasonality of deposition and to form a balance of particle transport at the annual time scale significant differences in total deposition were found over time ranging from 1 5 to 500 g dw m 2 d 1 including those between bare and vegetated sediments the effect of p oceanica in increasing primary deposition at an annual scale was modest however p oceanica significantly buffered sediment resuspension which was reduced more than three fold compared to the unvegetated bottom the annual flux of deposition was dominated by settling of resuspended materials which represented 85 of the total flux within the meadow but 95 of the total deposition on bare sand thus seagrass meadows reduce resuspension in the nw mediterranean littoral thereby contributing to increased sediment retention and therefore reducing erosion in the coastal zone

patterns in bioclastic accumulation through the phanerozoic changes in input or in destruction evolutionary changes in the ecology and diversity of organisms that produce and destroy calcareous skeletons suggest that bioclastic concentrations themselves might have changed in nature through the phanerozoic empirical data from marine siliciclastic records of ordovician silurian jurassic and neogene ages indicate a significant increase in the thickness of densely packed bioclastic concentrations over geologic time from a primarily thin bedded brachiopod dominated record in the ordovician silurian to a mollusk dominated record with many more and thicker shell beds in the neogene jurassic shell beds vary in thickness with the paleozoic or modern affinities of the chief constituents suggesting along with other evidence that the phanerozoic increase was determined neither by diagenesis nor by a shift in taphonomic conditions on the sea floor but rather by the evolution of bioclast producers namely groups with 1 more durable low organic skeletons 2 greater ecological success in high energy habitats and 3 on the basis of indirect evidence higher rates of carbonate production these results suggest that 1 reproductive and metabolic output has increased in benthic communities over time and 2 the scale of time averaging in benthic assemblages has increased owing to greater hard part durability of modern groups

glacial runoff and transport of suspended sediment from the chhota shigri glacier western himalaya india glacial runoff and suspended sediment transport characteristics of the chhota shigri glacier were studied during the whole ablation period may october 2010 discharge patterns of this glacier show that august experiences maximum runoff accounting for 34 2 of the total runoff followed by july 32 9 june 14 3 september 12 5 may 5 2 and october 0 9 during the study period the maximum runoff qmax was observed in the evening 4 6 p m whereas minimum runoff qmin was observed in the morning 7 9 a m the lag time between generation of meltwater from the glacier and its emergence as runoff varied from 1 to 4 h depending on the condition of melting during the melt season a good correlation r2 0 71 was found between daily mean glacier specific runoff and air temperature of the study area daily mean concentrations of suspended sediment for may june july august september and october were found as 155 506 577 591 80 9 and 30 8 mg l 1 respectively showing maximum concentration of suspended sediment in august followed by july suspended sediment load also follows a similar trend diurnal variations in the concentration of suspended sediment of the investigation area are directly associated with diurnal variations in meltwater runoff there is a strong relationship between concentration of suspended sediment and discharge r2 0 79 and suspended sediment load with discharge r2 0 94 the average sediment yield of the chhota shigri glacier basin was computed as 1689 t km 2 year 1 during the melt season much higher than the worldwide and indian averages

vertical variations of coral reef drag forces modeling flow in a coral reef requires a closure model that links the local drag force to the local mean velocity however the spatial flow variations make it difficult to predict the distribution of the local drag here we report on vertical profiles of measured drag and velocity in a laboratory reef that was made of 81 pocillopora meandrina colony skeletons densely arranged along a tilted flume two corals were ct scanned sliced horizontally and printed using a 3 d printer drag was measured as a function of height above the bottom by connecting the slices to drag sensors profiles of velocity were measured in between the coral branches and above the reef measured drag of whole colonies shows an excellent agreement with previous field and laboratory studies however these studies never showed how drag varies vertically the vertical distribution of drag is reported as a function of flow rate and water level when the water level is the same as the reef height reynolds stresses are negligible and the drag force per unit fluid mass is nearly constant however when the water depth is larger reynolds stress gradients become significant and drag increases with height an excellent agreement was found between the drag calculated by a momentum budget and the measured drag of the individual printed slices finally we propose a modified formulation of the drag coefficient that includes the normal dispersive stress term and results in reduced variations of the drag coefficient at the cost of introducing an additional coefficient

ecology of four infaunal bivalve species in the recent intertidal zone shikoku japan abstract spatial and density distributions mode of occurrence and size frequency histograms in living populations and death assemblages were analyzed quantitatively for four infaunal bivalve species on the intertidal flat of the coastal area of northwestern shikoku japan the results show that the mode of preservation of empty shells in the early process of fossilization differs greatly from species to species and or area to area the degree of taphonomic loss is low in deep burrowing species inhabiting muddy substrates and the spatial and density distributions and size frequency data of living populations are well preserved in the articulated empty shell assemblages in contrast dispersion of empty shells outside the habitat occurs frequently in the shallow infauna within coarser substrates this work suggests that articulated fossil shell assemblages of deep burrowing bivalves are probably autochtonous at the population level and that they may be most useful for detailed palaeoecological and palaeoenvironmental analyses

taphonomic windows and molluscan preservation recent studies on silicified fossil biotas have suggested that substantial skewing of the molluscan record resulted from early aragonite dissolution in mid outer carbonate ramp settings if those rare skeletal lagerstatten are representative then the quality and completeness of the molluscan record are thrown into doubt yet database studies suggest that the bivalve fossil record is actually relatively complete if so then biodiversity must be captured by other processes that preserved shells vulnerable to early dissolution and which operated on a relatively high frequency i e less than the species duration for bivalves storm beds shell plasters and submarine hardgrounds are identified as fossil deposits that can preserve the labile aragonitic component of the fauna and thus represent potential taphonomic windows many storm event beds include rich accumulations of shelly benthos differences between storm bed faunas and those of the background facies could reflect transportation effects however some storm bed assemblages are rich in originally aragonitic infaunal bivalves that are not represented in background facies or more proximal shelf equivalents and here rapid burial and removal of organic matter by winnowing may be the keys to aragonite shell preservation despite palaeozoic to cenozoic changes in the thickness and frequency of shell beds that reflect the predominant bioclast producers shallow infaunas are commonly concentrated together with epifauna in such deposits some low energy organic rich mud dominated settings are associated with preservation of aragonitic molluscs infaunal bivalves are a prominent component of shell plasters or pavements in such settings linked to episodic bottom water anoxia decaying algal blooms drew the redox boundary up above the sediment water interface and brought populations of infaunal bivalves to the surface where they died isolated from the oxic taphonomically active zone the shells were not dissolved and were buried as thin shell layers in similar settings aragonitic shells were preserved as moulds through early pyritisation or even through preservation of original shell aragonite in oxic environments bioturbational reworking of surface sediment destroyed moulds of aragonitic shells after early dissolution in some hardgrounds these delicate moulds were preserved due to synsedimentary cementation probably using carbonate released by aragonite dissolution the examples included here come from both intervals of calcite and aragonite seas and it is not possible to assess whether the saturation state with respect to aragonite of the ambient sea water played a role in the selective removal of aragonitic shells while taphonomic windows may have captured the diversity of individual groups it is clear from quantitative data involving skeletal lagerstatten that the scale of loss from early aragonite dissolution has drastically altered the trophic composition of some fossil assemblages commonly used as the basis for reconstructions of past communities

comments on the use of chemically based mixing models in glacier hydrology the assumptions involved in the use of chemically based mixing models for analysis of flow routing of meltwaters in glacierized basins are critically evaluated the assumption that glacial drainage systems consist of only two primary flow components is arbitrary and must be supported by independent evidence recent studies of the processes by which meltwaters acquire solute indicate that the assumption that flow components have unique and constant chemical compositions is unlikely to lie correct source water composition and weathering potential will vary over the course of a melt season and the extent of subglacial weathering is strongly dependent upon such factors as meltwater residence time and the availability of reactive sediment both of which are known to vary on diurnal to seasonal time scales mixing of flow components does not appear to be confined to the terminal regions of glaciers and is therefore unlikely to be conservative as assumed a multi parameter mixing model is applied to the analysis of data on the chemistry of waters sampled from bureholes drilled through haut glacier d arolla switzerland to demonstrate the range of dissolved species for which the assumption of conservative mixing is violated the consequences of this violation for quantitative hydrograph separation are shown to be highly significant the utility of mixing models as a tool for the investigation of glacier hydrological systems is questionable and the results of previous studies are unreliable

geographic gradients in the formation of shell concentrations plio pleistocene marine deposits gulf of california abstract shell bed coarse concentrations of invertebrate bioclastic material are rich sources of paleontologic and stratigraphic information studies often emphasize the relationship between shell bed formation and bathymetric gradients because many sedimentologic and ecologic factors that influence shell concentrating processes vary with water depth however shell bed formation is also influenced by factors that are not related to water depth shell beds in plio pleistocene marine sediments of the gulf of california mexico formed in less than 10 15 m water depth but under varying conditions of coastal topographic relief and tidal range sampling of shell beds focused on two regions the northern mainland coast and the southern peninsular coast shell beds in the northern mainland region 13 total formed along a macrotidal low relief coastline whereas shell beds in the southern peninsular region 27 total formed along a microtidal high relief coastline shell beds represent community beds 11 storm beds 3 beach berm beds 6 tidal channel bed 1 or current wave winnowed beds 19 the community beds represent biogenic concentrations the other four types represent sedimentologic concentrations sedimentologic concentrations formed either through short term concentrating events storm beds or long term dynamic bypassing beach berm beds tidal channel beds and current wave winnowed beds concentrations formed through dynamic bypassing are far more common 26 beds than storm concentrations 3 beds of the 26 concentrations formed through dynamic bypassing 10 cap major stratigraphic discontinuities representing temporal breaks ranging from 103 to 108 years the abundance and distribution of the five types of shell beds is significantly different between the two sampling areas the northern mainland coast is dominated by allochthonous beach berm beds capping linear beach ridges the formation of beach ridges in the north is favored by the wide shallow shelf representing a large reservoir for beach shells and sediment starved conditions resulting from the low topographic relief and periodic reductions in sediment supply from the colorado river delta beach berm beds are absent along the southern peninsular coast where coarse terrigenous sediment shed from adjacent highlands overwhelms shell input to the beach and the narrow steep shelf supplies the beach with few shells the southern peninsular coast is dominated by parautochthonous current wave winnowed beds and autochthonous community beds southern shell beds have undergone significantly less reworking winnowing and transportation than northern shell beds this is a function of both the relative weakness of tidal currents in the south and the relatively higher rates of terrigenous sedimentation along the rugged southern coastline which can bury shell concentrations relatively rapidly geographic variation in topographic relief and tidal range results in significant variation in the distribution and abundance of shell beds within these shallow marine sediments these variables have root tectonic cause relief reflects tectonic activity tidal range reflects basin configuration underscoring the potential utility of fossil concentrations for reconstructing earth history

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice i field evidence debris laden ice accretes to the base of matanuska glacier alaska u s a from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening frazil ice grows in the water column and forms aggregates while other ice grows on the glacier sole or on substrate materials sediment is trapped by this growing ice forming stratified debris laden basal ice growth rates of 0 1 m a 1 of debris rich basal ice are possible the large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings including heinrich events and the till sheets south of the laurentian great lakes

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

estimation of the bed shear stress in vegetated and bare channels with smooth beds the shear stress at the bed of a channel influences important benthic processes such as sediment transport several methods exist to estimate the bed shear stress in bare channels without vegetation but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production this study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds the model which is supported by measurements indicates that for both bare and vegetated channels with smooth beds within a viscous sublayer at the bed the viscous stress decreases linearly with increasing distance from the bed resulting in a parabolic velocity profile at the bed for bare channels the model describes the velocity profile in the overlap region of the law of the wall for emergent canopies of sufficient density frontal area per unit canopy volume a 4 3 m 1 the thickness of the linear stress layer is set by the stem diameter leading to a simple estimate for bed shear stress

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

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

the thermal and mechanical development of the wessex basin southern england summary the wessex basin of southern england is an e w trending late palaeozoic to tertiary extensional basin formed on early palaeozoic variscan crust extension occurred over a protracted period from late carboniferous to cretaceous times resulting in the evolution of four main depocentres or sub basins the channel basin winterborne kingston trough vale of pewsey and weald basins each sub basin was controlled fundamentally by the normal reactivation of basement thrust faults and wrench or transfer faults the basement faults represent primary structures associated with the fold and thrust terrain of the devonian carboniferous variscan orogeny subsequent but synchronous reactivation of both thrust and transfer faults tended to compartmentalize the basement leading to discrete depocentres and the production of general rhomboidal shaped sub basins characteristic of pull apart basins in strike slip terrains to investigate the thermo mechanical properties of the lithosphere during basin formation 50 boreholes within the wessex basin were back stripped to isolate the driving tectonic subsidence responsible for basin formation the resultant driving subsidence is characterized by a gentle sometimes negative exponential form with superimposed rapid discrete subsidence events as the geological development of the wessex basin was characterized by polyphase extension and the utilization of crustal detachments the lithospheric model used to determine crustal extension above the detachment and stretching below the detachment included the effects of depth dependent stretching and finite re rifting from the back stripping analysis the basin wide averaged upper crustal extension and lower crustal sub crustal lithospheric stretching were 11 and 5 respectively the distribution of is strongly influenced by the location of growth faults and hence basement thrust fault reactivation suggesting that is reflecting the brittle failure and collapse of hanging wall blocks repeated slip and block collapse resulted in the polyphase extension responsible for renewed basin subsidence in contrast is uniformly distributed across the basin suggestive of a ductile failure of the lower crust and responsible for the low magnitude thermal subsidence strain compatibility between the upper crust and lower crust sub crustal lithosphere is maintained partly within the basin 5 and partly external to the basin as the variscan basal thrust was the fundamental relay in the sense of wernicke responsible for the wessex basin formation we postulate that strain balancing induced a cumulative essentially thermal isostatic uplift of 60 m under the northern margin of the armorican massif

magnetostratigraphy of the lower cretaceous vectis formation wealden group on the isle of wight southern england magnetostratigraphic results are described from two sections within the lower cretaceous vectis formation formerly wealden shales of the isle of wight southern england the sections are located at shepherd9s chine and yaverland respectively in both of these sections a reliably established reverse polarity magnetozone herein defined as the vectis magnetozone occurs within the shepherd9s chine member this magnetozone has a thickness of some 15 m and its upper boundary is well defined in the yaverland section but is obscured in the shepherd9s chine section due to cliff slumping the lower boundary is well established in both sections and lies some 15 m above the barnes high sandstone member in the shepherd9s chine section and 12 m above this unit at yaverland this boundary provides a useful chron stratigraphic datum a comparison with established geomagnetic polarity timescales for the cretaceous indicates that the vectis magnetozone may be correlated either with lower aptian reverse polarity chron cm 0 or with lower barremian chron cm 1 with the former being the more likely an important implication of this interpretation is that the base of the aptian stage as defined from tethyan foraminiferal zones must lie within the vectis formation at least 25 30 m beneath the top of the shepherd9s chine member rather than at the top of this member as hitherto commonly accepted beds characterized by anomalously high intensities of magnetization which occur at the base of the vectis formation and a few metres above the barnes high sandstone in the two sections are tentatively interpreted as having a volcanogenic origin

estimating the distribution of suspended sediment concentration in submerged vegetation flow based on gravitational theory abstract vegetation plays a significant role in river ecosystem which has a great influence on hydraulic structures and sediment transport understanding the vertical distribution of suspended sediment concentration ssc in canopy flow is helpful to study the process of riverbed erosion and deposition in vegetated channels aiming at the sediment laden flow in open channel covered with submerged vegetation this study divides the water depth into two layers along the vertical direction with the vegetation height as the boundary and then proposes a new ssc distribution model based on gravitational theory to estimate the vertical distribution of relative ssc in the free water layer and vegetation layer respectively in the meanwhile a new formula is also proposed to evaluate the reynolds shear stress below the submerged vegetation height which has been successfully applied in the derivation of the new ssc distribution model the validation results of the simplified velocity model the new reynolds shear stress formula and the new ssc model compare well with the collected experimental data series on top of that it is found that the uniformity of ssc distribution profile progressively decreases with the increasing sediment particles diameters besides according to the validation results and discussion it is believed that the controversy point about gravitational theory would not have obvious influence on the estimation of ssc distribution so that the gravitational theory can be adopted to investigate suspended sediment transport in vegetation flow that would be benefit for river ecological restoration and better management

velocity distribution in the roughness layer of rough bed flows several models for the vertical distribution of the double averaged in time and in the plane parallel to the mean bed longitudinal velocity in the flow region between roughness troughs and roughness tops are suggested we found that the same model for velocity distribution may be applicable to a range of flow conditions and roughness types which share some common features the suggested models for velocity distribution in the near bed region are 1 constant velocity 2 exponential velocity distribution and 3 linear velocity distribution the measured velocity distributions may be approximated by a single model or by a combination of models depending on roughness geometry and flow conditions the validity of these models for velocity distribution is supported by laboratory data

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

black box modeling of the subglacial water system measurements of water pressure beneath trapridge glacier yukon territory canada yield the following generalizations about subglacial conditions in the studied region 1 even over short distances the subglacial water system is highly heterogeneous 2 the subglacial water system consists of at least two distinct components which we refer to as the connected and unconnected water systems 3 regions of the glacier bed can switch back and forth from being part of the connected or part of the unconnected water system 4 large spatial pressure gradients can exist within the unconnected water system and between the connected and unconnected systems 5 rapid pressure variations can occur in the unconnected water system 6 pressure variations in the unconnected water system do not match those in the connected system and can in fact be strongly anticorrelated with pressure variations in the connected system if the water pressure variations in the connected system are viewed as a forcing and those in the unconnected system as a response to this forcing the input output relation between forcing and response can be efficiently represented as a low order nonlinear ordinary differential equation the response of the unconnected system to forcing from the connected system is governed by time constants having approximate magnitudes of 1 7 hours and 7 4 hours that we believe are associated with process rates for substrate compression and pore water diffusion respectively

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

seabed stress determinations using the inertial dissipation method and the turbulent kinetic energy method direct measurements of seabed stress are difficult especially in field conditions several methods for estimating these stresses using current meter data are available two of these methods the inertial dissipation method and the turbulent kinetic energy method are described below and a matlab program is used to analyse data from a wave current environment

flow and deposition in and around a finite patch of vegetation this laboratory study describes the flow and deposition observed in and around a finite patch of vegetation located at the wall of a channel two patch densities are considered with 2 and 10 solid volume fraction the velocity field measured in and around the patch by acoustic doppler velocimetry revealed three distinct zones first there is a diverging flow region at the leading edge of the patch where the flow in line with the patch decelerates and the bulk of the flow is diverted toward the open channel second there is a fully developed region within the vegetation where the velocity is uniform across the patch width and along the length of the patch third a shear layer forms at the interface between the patch and adjacent open channel the pattern of deposition in and around the vegetation was characterized by releasing 12 micron spherical glass particles and recording net deposition on a set of glass slides in the diverging region net deposition increases in the stream wise direction as the local velocity decreases in the fully developed region of the patch deposition decreases with longitudinal position as the concentration in the water column is depleted the deposition pattern is nearly uniform across the patch width consistent with the velocity field and suggesting that turbulent diffusive flux across the lateral edge of the patch is not a significant source of particles to the patch under the conditions studied here

internal geometry and evolution of moulins storglaciaren sweden depart ment of physical geog raphy university of stoc kholm s 106 91 stockholm sweden abstract the initial conditions needed for formation of moulins are crevasses and a supply of melt water water pouring into a crevasse may fill it until it ove rflows at the lowest point which is normally near the margin however as the crev asse deepens it intersects englacial chann els through which the water can drain these chann els may be finger tip tributaries in a dendritic system such as that described by shreve 1972 and observ ed by raymond and harrison 1975 when the cre vasse closes heat in the melt water keeps the conne ction open and a moulin is formed the englacial channel enlarges rapidly by melt ing utilizing mechanical energy released by the descending water descents into moulins and mapping of stru ctures exposed at the surface after many years of melting demonstrate that the drainage channels leading down from the bottoms of the moulins have incli nations of 0 450 from the vertical these channels trend in the dire ction of the original crevasse but appear to be deeper than the expected depth of the crevasse they have not

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

borehole water level variations and the structure of the subglacial hydrological system of haut glacier d arolla valais switzerland late summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of haut glacier d arolla switzerland interpolated surfaces of minimum diurnal water pressure and diurnal water pressure variation suggest the presence of a subglacial channel within a more widespread distributed drainage system the channel flows along the centre of a variable pressure axis vpa some tens of metres wide that is characterized by low minimum diurnal water pressures frequently atmospheric and high diurnal water pressure variations these characteristics are transitional over a lateral distance of c 70 m to higher and more stable subglacial water pressures in the adjacent distributed system water pressure variations recorded in boreholes located close to the centre of the vpa reflect the delivery of surface derived meltwater to the glacier bed and result in a diurnally reversing transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight subglacial observations suggest that such flow occurs through a vertically confined sediment layer borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension analysis of the propagation velocity and amplitude attenuation of the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel falling from c 10 4 m s 1 at the channel boundary to c 10 7 ms 1 70m away these apparent hydraulic conductivities are consistent with darcian flow through clean sand and typical glacial till respectively we suggest that fine material is systematically flushed from basal sediments located adjacent to large melt season drainage channels beneath warm based glaciers this process may have important implications for patterns of glacier erosion hydrochemistry and dynamics

evolution of drainage system morphology at a land terminating greenlandic outlet glacier 1 the influence of meltwater on the dynamics and geomorphic impact of the greenland ice sheet is strongly controlled by the morphology of the ice sheet s drainage system however this system and its evolution through the melt season remain poorly understood here we present the results of an intensive programme of dye tracing experiments undertaken along the lower 14 km of a land terminating greenlandic outlet glacier over a period of four months during the 2010 melt season these data are interpreted in conjunction with observations of proglacial discharge englacial water storage surface melt rates and ice velocity to produce a detailed picture of the changing hydrology of the glacier following the onset of melt in the spring inputs to the drainage system regularly exceed outputs causing the englacial water level to rise to the ice sheet surface during this time there is a rapid transition from distributed to channelized drainage in those parts of the drainage system closed by ice deformation over winter as the melt season progresses channel efficiency increases and englacial storage and ice velocity decrease high velocity events continue to be observed following the channelization of the drainage system however indicating that hydrological forcing of ice velocity occurs despite the existence of channels during periods when meltwater inputs exceed the capacity of the subglacial drainage system

an experimental study of flow through rigid vegetation 1 better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation instead of spatial averaging this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels velocity data was collected with a one dimensional laser doppler velocimeter under emergent and submerged flow conditions the effects of dowel arrangement density and roughness were also examined the results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it however the boundaries are marked by inflection points the strongest vortices and turbulence intensities can be found there especially in the region immediately downstream of a dowel these results support the idea that the flow in the region near the bed and at the top of the dowel array is very unstable leading to the formation of coherent structures and are areas of significant mass and momentum exchange

investigations of glacier hydrological systems using dye tracer techniques observations at pasterzengletscher austria a l aide de traceurs colores on a mis en evidence une division laterale du drainage dans le bas de la langue qui n est pas determinee par la direction des crevasses obliques la reapparition de l eau dans les differents moulins est complexe bien qu elle reste constante dans le temps

significance of molluscan shell beds in sequence stratigraphy an example from the lower cretaceous mannville group of canada1 detailed study of marine shales the ostracod zone within a cretaceous third order transgressive regressive sequence in the alberta foreland basin reveals a systematic association between shell beds and parasequence scale flooding surfaces including surfaces of maximum flooding the ostracod zone a subsurface lithostratigraphic unit known as the calcareous member in outcrop consists of 10 20 m of black shale and bioturbated sandstones with many thin fossiliferous limestones parasequences shallowing up cycles 2 3 m thick were delineated within this transgressive unit based on lithology sedimentary structures degree of bioturbation dinoflagellate diversity total organic carbon and carbon sulphur ratios many flooding surfaces are firmgrounds or hardgrounds shell rich limestones occur in three different positions relative to these flooding surfaces and each has a distinctive bioclastic fabric and origin i base of parasequence shell beds bops lie on or just above flooding surfaces in the deepest water part of a parasequence they are thin up to a few centimetres graded or amalgamated skeletal packstones wackestones composed of well sorted granular shell and are interpreted as hydraulic event concentrations of exotic shell debris ii top of parasequence shell beds tops are capped by flooding surfaces at the top shallowest water part of a parasequence they typically are several decimetres thick are physically amalgamated packstones grainstones or bioturbated wackestones and contain abundant whole as well as comminuted shells these are composite multiple event concentrations of local shells iii mid sequence shell beds rest on as well as are capped by firmgrounds or hardgrounds and are intercalated between parasequences in the deepest water part of the larger sequence they are laterally extensive lime mudstones a few decimetres thick with sparse shells in various states of dissolution recrystallization and replacement these beds are terrigenous starved hiatal concentrations and record maximum flooding within the ostracod zone offshore sections of the ostracod zone typically contain several starved mid sequence shell beds underscoring the difficulty of identifying a single maximum flooding surface within a third order sequence

shell beds as tools in basin analysis the jurassic of kachchh western india skeletal concentrations are ubiquitous in bathonian oxfordian shallow water sediments of the pericratonic basins of kachchh and rajasthan western india by analysing the biofabric of the concentrations and the taphonomic signatures of individual components it is possible to distinguish between the final concentration process recorded by the biofabric and events taking place prior to final deposition recorded by taphonomic signatures the skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations they mainly reflect biological and hydraulic processes and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient plotted against the stratigraphic sections the skeletal concentrations show in accordance with other sedimentological data three orders of bathymetric trends the first two orders are shallowing deepening cycles which possibly correspond to eustatic changes in sea level the third order represents parasequences with a strongly asymmetric sedimentary record skeletal concentrations are a useful additional tool in basin analysis but are best used in combination with other data