greenland meltwater as a significant and potentially bioavailable source of iron to the ocean the micronutrient iron is thought to limit primary production in large regions of the global ocean meltwater measurements suggest that the greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

interaction among alluvial cover bed roughness and incision rate in purely bedrock and alluvial bedrock channel a major control on bedrock incision is the interaction between alluvial cover and erosive mobile grains the extent of alluvial cover is typically predicted as a function of relative sediment flux sediment supply rate over bed load transport capacity qbs qbc yet little is known about how the bed roughness affects the alluvial cover we performed field experiments with various flow discharges sediment supply rates grain sizes and bed surface topographies we then developed physically based models for estimating the threshold of sediment movement and the extent of alluvial cover so as to include the effect of roughness change the results for the threshold of sediment movement and the extent of alluvial cover obtained from our models show reasonable agreement with the results of the field experiments we explored the sensitivity of the models to variations in sediment supply and bedrock relative roughness bedrock hydraulic roughness height over grain size ksb d the results suggest the following 1 a larger relative roughness yields a greater dimensionless critical shear stress required for initial sediment motion 2 at a given sediment supply rate the extent of alluvial cover is larger when the relative roughness is larger 3 when the sediment supply rate and the relative roughness are small throughput bed load moves over and can abrade a purely bedrock channel with no alluvial cover and 4 the critical value of sediment supply rate below which throughput bed load transport occurs increases with decreasing relative roughness the experimental results and analysis provide a framework for treating the a incisional morphodynamics of purely bedrock rivers by throughput bed load with no alluvial cover b incisional alluvial morphodynamics of mixed bedrock alluvial rivers and c purely alluvial morphodynamics as well as the transition between these states

deepening of inner gorges through subglacial meltwater an example from the unesco entlebuch area switzerland this paper explores the mechanisms by which inner gorges in the alps were formed it focuses on the ca 1 5 km long 80 m deep and a few hundred meter wide lammschlucht located in the northern foothills of the central alps we reconstructed the glacial cover using lateral moraines and hanging talus cones that record the elevation of the ice surface at the deglaciation stage of the lgm last glacial maximum we used the reconstructed ice thickness patterns to calculate the erosional potential of the subglacial meltwater the applied model is based on the principle of energy conservation and yields the pattern of downstream changes of the dynamic pressure which is considered a measure for erosion potential the model results suggest a maximum of the dynamic pressure at the end of the inner gorge we interpret therefore that the subglacial meltwater scoured the reach toward the end of the lammschlucht because of the enhanced dynamic pressure which was ultimately controlled by the ice overburden post glacial fluvial erosion then resulted in a readjustment through a regressive shift of the erosional front along the inner gorge farther upstream the current location of this front lies almost in the middle of the lammschlucht inner gorge where a step pool channel changes into a straight plane bed channel flowing on a deeply scoured bedrock

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

palynology sedimentology and palaeoecology of the late holocene dead sea abstract palynological and sedimentological studies were performed at two holocene profiles in erosion gullies ze elim and ein feshkha which dissect the retreating western shore of the dead sea the aim of the project was to analyse possible links between climate lithology and vegetation development the section in ze elim shows both lacustrine and fluvial sediments whereas sedimentation at ein feshkha is predominantly lacustrine the ze elim profile previously used for paleo lake reconstruction provides an opportunity to compare climate triggered lake levels as paleo hydrological indicators and vegetation history by use of palynology the vegetation development in ze elim and ein feshkha is influenced by both climate and human impact the pollen record of ze elim begins in the pottery neolithic the section of ein feshkha in the late bronze age both records end in the middle ages the ze elim section is characterized by sedimentary hiati between the beginning of the chalcolithic period until the middle bronze age and within the late bronze age settlement periods during the middle bronze age iron age and hellenistic roman byzantine period are indicated by high values of anthropogenic indicators and or mediterranean trees collapses of agriculture which can be related to climate effects are evident during the late bronze age during the iron age and at the end of the byzantine period when the lake level curve indicates arid conditions a comparison of the two pollen records from different environments illustrates a more prominent influence of mediterranean vegetation and cultivated plants in the pollen diagram of ein feshkha the southern dead sea region at the desert fringe is more vulnerable to regional climate change

medieval warming little ice age and european impact on the environment during the last millennium in the lower hudson valley new york usa establishing natural climate variability becomes particularly important in large urban areas in anticipation of droughts we present a welldated bi decadal record of vegetation climate land use and fire frequency from a tidal marsh in the hudson river estuary the classic medieval warm period is evident through striking increases in charcoal and pinus dominance from 800 1300 a d paralleling paleorecords southward along the atlantic seaboard higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions the presence of the little ice age ensues with increases in picea and tsuga coupled with increasing organic percentages due to cooler moister conditions european impact is manifested by a decline in arboreal pollen due to land clearance increased weedy plant cover i e ambrosia plantago and rumex and an increase in inorganic particles to the watershed

holocene palaeoecology of the golan heights near east investigation of lacustrine sediments from birkat ram crater lake abstract lacustrine deposits of the crater lake birkat ram located in the northern golan heights have been used as a paleoecological archive preliminary sedimentological and palynological investigations based on a composite profile allow the reconstruction of the environmental history of the last 6500 years fluctuations of the pollen composition trees and shrubs versus herbs values of oak and olive tree correspond to changes in different sediment parameters total organic carbon magnetic susceptibility which can be interpreted as the effects of human impact on the geo biosphere four phases with strong settlement activities can be identified for the northern golan heights 1 during the chalcolithic period early bronze age 2 during the hellenistic roman byzantine periods 3 during the crusader period and finally during modern time these periods were interrupted by wooded regeneration phases with low anthropogenic activities

erosion by an alpine glacier assessing the impact of glaciation on earth s surface requires understanding glacial erosion processes developing erosion theories is challenging because of the complex nature of the erosion processes and the difficulty of examining the ice bedrock interface of contemporary glaciers we demonstrate that the glacial erosion rate is proportional to the ice sliding velocity squared by quantifying spatial variations in ice sliding velocity and the erosion rate of a fast flowing alpine glacier the nonlinear behavior implies a high erosion sensitivity to small variations in topographic slope and precipitation a nonlinear rate law suggests that abrasion may dominate over other erosion processes in fast flowing glaciers it may also explain the wide range of observed glacial erosion rates and in part the impact of glaciation on mountainous landscapes during the past few million years

a coupled sheet conduit mechanism for jokulhlaup propagation 1 the largest glacier outburst flood jokulhlaup ever recorded in iceland occurred in 1996 and came from subglacial lake grimsvotn in vatnajokull ice cap among other noteworthy features this flood was characterized by an unprecedentedly high lake level prior to flood initiation extremely rapid linear rise in lake discharge delay between the onset of lake drainage and floodwater arrival at the glacier terminus formation of short lived supraglacial fountains and initially unchannelized outbursts of floodwater at the terminus observations suggest that the 1996 flood propagation mechanism was fundamentally different than that of previously observed floods from grimsvotn we advance a new model whereby floodwater initially propagates in a turbulent subglacial sheet which feeds a nascent system of conduits this model is able to explain key observations made of the 1996 jokulhlaup and may shed light on other outburst floods that do not conform to the standard model

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products publisher elsevier articletitle theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products journaltitle earth science reviews articlelink http dx doi org 10 1016 j earscirev 2016 01 010 content type article copyright copyright 2016 elsevier b v all rights reserved

mechanical properties of hydrate bearing turbidite reservoir in the first gas production test site of the eastern nankai trough abstract the study of mechanical properties of marine sediments is essential for the prediction of the occurrence of geohazards e g subsea landslides and seafloor subsidence and the design of submarine structures for offshore industry in this study triaxial compression tests of gas hydrate bearing sandy sediments and clayey silty sediments were conducted the sediments were recovered by pressure coring in the eastern nankai trough the area of the first japanese offshore production test soil index properties were measured and revealed porosity of 40 50 with porosity decreasing gradually with greater depth below the seafloor the mean particle size was less than 10 m for clayey silty sediments and approximately 100 m for sandy sediments permeability estimated by a consolidation process of triaxial testing and with x ray diffraction analysis depended on the content of fines which consisted chiefly of mica kaolinite and smectite the results of undrained compression tests for clayey silty sediments showed positive excess pore pressure under all test conditions this mechanical behavior indicates that the core samples are normally consolidated sediments drained compression tests showed that the strength and stiffness of sandy sediments increase with hydrate saturation furthermore the volumetric strain of hydrate bearing sediments changed from compression to dilative this result was obtained for hydrate saturation values sh of more than 70 the shear strength of hydrate bearing turbidite sediments of the eastern nankai trough is shown to be a function of the confining pressure

hydraulics of subglacial outburst floods new insights from the spring hutter formulation using a slightly modified form of the spring hutter equations glacial outburst floods are simulated from three classic sites hazard lake yukon canada summit lake british columbia canada and grimsvotn iceland in order to calibrate the hydraulic roughness associated with subglacial conduits previous work has suggested that the manning roughness of the conduits is remarkably high but the new calibration yields substantially lower values that are representative of those for natural streams and rivers the discrepancy can be traced to a poor assumption about the effectiveness of heat transfer at the conduit walls the simulations reveal behaviour that cannot be interred from simplified theories 1 during flood onset water pressure over much of the conduit can exceed the confining pressure of surrounding ice 2 local values of fluid potential gradient can differ substantially from the value averaged over the length of the conduit contradicting an assumption of simple theories 3 as the flood progresses the location of flow constrictions that effectively control the flood magnitude can jump rapidly over large distances 4 predicted water temperature at the conduit outlet exceeds that suggested by measurements of exit water temperature

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

the relative efficacy of fluvial and glacial erosion over modern to orogenic timescales it has been debated whether rivers or glaciers are more effective agents of erosion a global compilation of erosion rates reveals that both are capable of generating rates of erosion that match or exceed the highest rates of rock uplift since the late nineteenth century it has been debated whether rivers or glaciers are more effective agents of erosion1 the dramatic landscapes associated with glaciated terrain have often led to the argument that glaciers are more erosive than rivers and recent studies have documented the topographic signature of an ice controlled limit of mountain height known as the glacial buzz saw 2 3 here we present a new global compilation of erosion rates which questions the conventional view of glaciers and erosion in regions of rapid tectonic uplift erosion rates from rivers and glaciers both range from 1 to over 10 mm yr 1 indicating that both are capable of generating erosion rates matching or exceeding the highest rates of rock uplift moreover a comparison of erosion rates over timescales ranging from 101 to 107 years indicates that glacial erosion tends to decrease by one to two orders of magnitude over glacial cycles whereas fluvial erosion rates show no apparent dependence on time we conclude that tectonics controls rates of both fluvial and glacial erosion over millennial and longer timescales and that the highest rates of erosion 10 mm yr 1 generally result from a transient response to disturbance by volcanic eruptions climate change and modern agriculture

cold and dry outbreaks in the eastern mediterranean 3200 years ago can climate affect societies this question of both past and present importance is encapsulated by the major socioeconomic crisis that affected the mediterranean 3200 yr ago the demise of the core civilizations of the aegean and eastern mediterranean during the late bronze age and the early iron age dark ages is still controversial because it raises the question of climate change impacts on ancient societies although evidence for this climate shift has gradually gained currency recent attempts to quantify its magnitude remain equivocal here we focus on the northern levant coastal syria where the economic political and cultural changes were particularly acute we quantify past climate changes and find that mean annual temperatures attained anomalies of 2 3 0 3 degrees c to 4 8 0 4 degrees c compared to present day conditions rainfall regimes displayed an important shift in seasonality with a 40 decrease in winter precipitation a 300 yr period of dry and cool climate started similar to 3200 yr ago and was coeval with deep social changes in the eastern mediterranean these little ice age type conditions affected harvests leading to severe food shortages that probably aggravated the sociopolitical tensions this crisis highlights the fragility of societies both past and present to major climate change episodes and their broader consequences

sedimentology of the nw margin of the arabian plate and the sw ne trending nahr el kabir half graben in northern syria during the latest cretaceous and cenozoic abstract the late cretaceous maastrichtian to recent sedimentary record of nw syria documents the palaeoenvironments and regional tectonic setting during a time when the neotethys ocean to the north was closing culminating in regional collision by mid miocene time this detailed sedimentological study builds on a biostratigraphical framework established by russian workers during the mid maastrichtian the baer bassit ophiolite and related melange were emplaced southwards from neotethys onto the northern margin of the arabian african plate resulting in flexurally controlled deepening to the south after short lived emergence and erosion of emplaced units a renewed marine transgression ushered in shelf depth open marine carbonate deposition during the palaeocene early eocene this deposition was characterized by generally westward channelised mass flow from shallow marine carbonate banks to the east probably influenced by storm conditions flexurally controlled uplift and erosion took place during late eocene oligocene related to final closure of neotethys shelf depth carbonate deposition resumed during the aquitanian early miocene influenced by tectonic subsidence during the burdigalian a sw ne trending narrow up to 15 km wide linear 60 km long basin developed in the vicinity of the present day nahr el kabir river valley this basin is attributed to extension or transtension along the nahr el kabir fault this important lineament runs onshore from the southern limit of the cyprus arc tartous ridge through nw syria it is then offset by the dead sea transform in the ghab valley before merging with the south anatolian transform fault in turkey further northeast the basin in nw syria developed into the asymmetrical nahr el kabir half graben during the mid miocene with uplift of the northern margin and rapid fault controlled subsidence of the basin axis large volumes of terrigenous clastic and shallow marine bioclastic material were redeposited from the flanks into the axis of the basin mainly as gravity flows shelf depth carbonate deposition characterized both basin flanks especially the southern margin regression culminated in gypsum and marl precipitation in tectonically active local depocentres during the messinian salinity crisis pliocene re flooding established argillaceous shelf deposition within and around the pre existing basin coupled with local alkaline basalt volcanism and faulting in the southern coastal area regional regression gave rise to prominently channelised bioclastic sedimentation by the late pliocene the quaternary was marked by regional uplift and terracing influenced by glacio eustatic sea level change climatic change and further movement along the nahr el kabir fault the dominant control on basin development was thus local tectonics related to movements along the el kabir lineament and its interaction with regional scale tectonic events while eustasy played a subsidiary modifying role

sediment evacuation and glacial erosion rates at a small alpine glacier 1 glacial erosion is known to be driven by sliding which occurs in brief episodes in the melt season what is not known is how well this sliding history is reflected in the sediment output from a glacier and to what degree temporary sediment storage in the glacier smoothes the history of sediment production we document sediment evacuation rates for three seasons at bench glacier a small temperate alpine glacier in the chugach range of alaska two lines of evidence suggest that subglacial sediment storage is small strong hysteresis in the relationship between sediment and water discharge argues for sediment exhaustion from the subglacial system on seasonal and flood event timescales uplift of the glacier surface during periods of enhanced basal motion reflects intimate contact of the glacier sole with up glacier inclined stoss slopes of bedrock bumps sediment evacuation rates at bench glacier should therefore closely track glacial erosion rates over annual timescales much of the sediment emerges in a major pulse that closely follows the termination of enhanced sliding each year suggesting that the conduits and well connected cavities that allowed removal of englacial water to terminate sliding also promoted efficient transport of sediment this small glacier efficiently modifies the landscape lowering its bed by 1 2 mm yr while sliding only 1 2 m yr our sparse measurements of instantaneous bed load discharge average 41 of concurrent suspended sediment discharge assuming that half of the suspended load derives from abrasion of subglacially quarried clasts roughly two thirds of the sediment evacuated can be attributed to quarrying

global climate instability reflected by eastern mediterranean marine records during the late holocene abstract extremely high sediment accumulation rates in the southeastern se mediterranean off israel make this region ideal for high resolution paleoceanographic reconstructions two cores were examined and foraminiferal oxygen and carbon isotope composition as well as physical and geochemical properties of the sediments were used to reconstruct the climatic and environmental changes of the se mediterranean basin during the late holocene 3 6 ka the 18o values of globigerinoides ruber suggest that the freshwater balance changed several times during this time interval humid phases took place between 3 5 3 0 ka bp and 1 7 1 0 ka bp the later was accompanied by enhanced preservation of terrestrial organic matter within the sediment ors event relatively more arid conditions prevailed in this area between 3 0 and 1 7 ka bp during the last millennia at ca 0 8 and 0 27 ka two climatic events occurred which are probably correlative to both the medieval warm period and the cooling global event known as the little ice age respectively a long term slight increase in planktonic foraminiferal 18o values occurs together with a gradual decrease in the 13c values of both g ruber and the benthic foraminifera uvigerina mediterranea this trend is associated with an increase in sedimentation rates ti al ratio magnetic susceptibility and color index of the sediments we suggest that this trend shown by various independent proxies seems to be related to the aridification process that started ca 7 0 ka in the mid low latitude desert belt and the se mediterranean region and continuous until the present the long term 13c decrease shown by surface and bottom water foraminifera reflects a gradual change in the 13c of the dissolved co2 of the entire se mediterranean water column this follows the global co2 rise in the late holocene as a result of the terrestrial biomass destruction during the aridification process moreover the gradual reduction of the vegetation cover in east africa led to an increased erratic flood related sediment flux via the nile river up to the present this is reflected by the general change in the local sediment composition at 3 6 ka the saharan eolian input reached 65 whereas at about 0 3 ka 70 of the se mediterranean sediment was composed of nile particulate matter

experimental research on the mechanical properties of methane hydrate bearing sediments during hydrate dissociation abstract this paper describes studies of the effect of hydrate dissociation on the safety and stability of methane hydrate bearing sediments methane hydrates within the sediments were dissociating under the conditions of a confining pressure of 0 5 mpa 1 mpa 2 mpa and a temperature of 5 c after 6 h 24 h or 48 h a series of triaxial compression tests on methane hydrate bearing sediments were performed the tests of ice clay and sediments without hydrate dissociation were performed for comparison focusing on the mechanical properties of the sediments the experimental results indicated that the shear strength of the ice clay mixtures was lower than that of the methane hydrate bearing sediments the strength of the sediments was reduced by hydrate dissociation and the strength tended to decrease further at the lower confining pressures the secant modulus e s of the sediments dropped by 42 6 in the case of the dissociation time of the hydrate of 48 h at the confining pressure of 1 mpa however the decline of the initial yield modulus e 0 was only 9 34 the slower hydrate dissociation rate contributed to reducing the failure strength at a declining pace based on the mohr coulomb strength theory it was concluded that the decrease in strength was mainly affected by the cohesive reduction moreover the mathematical expression of the m c criterion related to the hydrate dissociation time was proposed this research could be valuable for the safety and stability of hydrate deposits in a permafrost region

subglacial drainage eskers and deforming beds beneath the laurentide and eurasian ice sheets glaciological theory predicts that the subglacial drainage network at the base of gently sloping ice sheets resting on deforming sediment should consist of many wide shallow probably braided canals distributed along the ice sediment interface rather than an arborescent network of relatively few large tunnels as would develop over a rigid substrate a corollary prediction examined here is that eskers which form in large subglacial tunnels should be rare where subglacial bed deformation occurred but they may be relatively common where the bed was rigid bed deformation would be most likely where subglacial till was relatively continuous fine grained and of low permeability that is in regions where till is derived primarily from underlying sedimentary bedrock but unlikely where discontinuous coarse grained high permeability till was derived from underlying crystalline bedrock the observed distribution of eskers in areas covered by the laurentide and eurasian british scandinavian and barents sea ice sheets during the last glaciation shows that most eskers occur over crystalline bedrock overlain by discontinuous high permeability till but are rare or absent over sedimentary bedrock overlain by fine grained low permeability till thus matching reasonably well our prediction glaciological theory and geologic evidence indicate that esker systems on a subcontinental scale are time transgressive sedimentological evidence for a canal drainage system appears to be present in fine grained tills where eskers are largely absent

a theoretical framework for the morphodynamics of bedrock channels 1 bedrock rivers are characterized by conditions of insufficient sediment supply wherein the amount of sediment supplied to the channel is less than the channel s sediment transport capacity consequently bedrock channels generally exhibit discontinuous sediment cover which current approaches to the morphodynamics of alluvial rivers are unable to handle to fill this gap we present a theoretical framework in which local sediment transport rates are proportional to the areal concentration of sediment available for transport on the bed and the sediment continuity equation is reformulated to account for temporal changes in areal concentration of sediment on nonalluviated surfaces we then perform a linear stability analysis that shows that an initially uniform distribution of the areal concentration of sediment on the bed is unstable to small perturbations this suggests that the sediment cover in bedrock channels tends to concentrate into regions which may eventually be alluviated in general agreement with experimental observations

a late bronze age site and fluvial environmental context in the middle euphrates valley northeast syria alluvial sediments provide records of environmental changes when early civilisations were born on mesopotamian floodplains during approximately 6 kyr bp in this work we study and date the alluvial infill of a palaeochannel and sediments of a neighbouring wadi that flowed into the middle euphrates such a palaeochannel is alongside an archaeological site abandoned in the late bronze age ii it was a strategic control point of the river transit in that period when a single meandering channel existed we hypothesise that the site was not reoccupied after destruction by a fire because of the loss of geostrategic interest as it remained far from the new river channel the main river channel was moved and the palaeochannel filled with flash flood sediments possibly because of natural or human induced environmental changes optically stimulated luminescence osl allows direct dating of alluvial sediments but it has been little tested in this area while both radiocarbon and pottery style dating have bee

how glaciers entrain and transport basal sediment physical constraints abstract simple insights from the physics of ice water and sediment place constraints on the possible sediment transport behavior of glaciers and ice sheets because glaciers concentrate runoff streams generated by glaciers transport much sediment and may erode bedrock rapidly deforming glacier beds also can transport much sediment particularly in marginal regions rapid sediment entrainment producing thick debris rich basal zones may occur by regelation into subglacial materials and by freeze on from rising supercooled waters numerous other mechanisms may be important but primarily near ice margins especially those of advancing or fluctuating glaciers several sediment entrainment mechanisms may be active beneath a single glacier but one process is likely to be dominant at any place and time

tunnel valleys current knowledge and future perspectives tunnel valleys are elongated incisions that are commonly interpreted as being the result of erosional processes by subglacial meltwater occurring under continental ice sheets the abundance size and the primarily coarse grained infill of these features have made tunnel valleys important hydrocarbon and groundwater reservoirs although numerous tunnel valleys have been described over the last century their formation and infill remain poorly understood this review summarizes and discusses the current knowledge of tunnel valleys providing an overview of the observations around the world morphological aspects that separate tunnel valleys from other landforms are discussed as well as the wide variety of sedimentary environments found to contribute to the infilling of these features the depth of the incision and the character of ice retreat significantly determine the final infill architecture the formational hypotheses proposed in the literature are assessed to test their wider applicability to all other tunnel valleys in order to find a generic model that helps in the prediction of the morphology and infilling of both pleistocene and pre pleistocene age a quasi steady state model with small meltwater outbursts that erode tunnel valleys near the ice margin seems compatible with most of the known valleys other proposed models require specific geographical or climatic conditions

hydrate adhesive and tensile strengths the physical properties of hydrate bearing sediments depend on the interaction between hydrates and minerals in particular hydrates prefer to nucleate on mineral surfaces therefore the hydrate mineral adhesive strength and the tensile strength of the hydrate mass itself affect the mechanical response of hydrate bearing sediments in this study ice and hydrates made with various guest molecules co2 ch4 and thf are formed between mica and calcite substrates adhesive and tensile strengths are measured by applying an external pull out force results show that tensile failure occurs in co2 and ch4 hydrates when calcite is the substrate while ice and all hydrates exhibit adhesive failure on mica the debonding strength is higher when calcite substrates are involved rather than mica substrates a nominal pull out strength of 0 15 0 03 mpa can be adopted for mechanical analyses of hydrate bearing sediments

experimental investigation of gas water relative permeability for gas hydrate bearing sediments from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract permeability of hydrate reservoirs found in nature is likely to be heavily influenced by the percent of the pore volume occupied by hydrates the quantification of how hydrate saturation affects permeability is of key interest for reservoir engineering studies in this study an experimental setup was modified to test permeability characteristics of unconsolidated core samples containing various saturations of methane hydrates hydrates were formed in the unconsolidated samples using a refrigerated core holder connected to a brine and methane injection system studies of this type conducted to date have rarely been performed on core samples recovered from actual hydrate bearing sedimentary sections from natural hydrate intervals samples from the mount elbert site on the alaska north slope ans were used for this study relative permeability measurements using hydrate constituent components e g water and methane are not very desirable due to difficulties in preventing additional hydrate formation during displacement experiments relative permeability measurements performed with hydrate constituent components e g water and nitrogen can help to significantly mitigate issues with additional hydrate formation however unsteady state relative permeability experiments produce piston like displacement results suggesting that steady state experiments might be preferable it was observed that as in previous work using consolidated core samples permeability of both brine and gases was reduced in unconsolidated hydrate bearing core samples experimental results show that low to moderate hydrate saturations 1 5 to 36 can significantly reduce permeability of porous media these saturations in fact are lower than hydrate saturations observed in the natural hydrate systems at mount elbert

middle east coastal ecosystem response to middle to late holocene abrupt climate changes the holocene vegetation history of the northern coastal arabian peninsula is of long standing interest as this mediterranean semiarid arid region is known to be particularly sensitive to climatic changes detailed palynological data from an 800 cm alluvial sequence cored in the jableh plain in northwest syria have been used to reconstruct the vegetation dynamics in the coastal lowlands and the nearby jabal an nusayriyah mountains for the period 2150 to 550 b c corresponding with the 4 2 to 3 9 and 3 5 to 2 5 cal kyr bp abrupt climate changes accs two large scale shifts to a more arid climate have been recorded these two accs had different impacts on the vegetation assemblages in coastal syria the 3 5 to 2 5 cal kyr bp acc is drier and lasted longer than the 4 2 to 3 9 cal kyr bp acc and is characterized by the development of a warm steppe pollen derived biome 1100 800 b c and a peak of hot desert pollen derived biome at 900 b c the 4 2 to 3 9 cal kyr bp acc is characterized by a xerophytic woods and shrubs pollen derived biome ca 2050 b c the impact of the 3 5 to 2 5 cal kyr bp acc on human occupation and cultural development is important along the syrian coast with the destruction of ugarit and the collapse of the ugarit kingdom at ca 1190 to 1185 b c

post little ice age record of coarse and fine clastic sedimentation in an alaskan proglacial lake many assessments of glacial sediment yield rely solely on mea surements of fine grained suspended sediment we show that sus pended sediment contributes 20 of the total clastic sediment discharge into iceberg lake an alaskan proglacial lake drainage of this lake in 1999 exposed outcrops of varved lacustrine sediment that record suspended sediment deposition since a little ice age highstand two centuries ago lake level has dropped in four abrupt spillway controlled events that are recorded stratigraphically as transient increases in the basinwide deposition of unusually fine grained sediments varve counting constrains ages of these events and hence of each abandoned shoreline and associated delta vol umes of deltaic and lake floor sediments constrain specific yields from four multidecadal intervals between a d 1825 and 1999 to tal yield ranges from 3 8 to 4 9 3 10 3 t km 22 yr 21 and most of the sediment 81 86 is sand and gravel now in the deltas a range of evidence suggests that sediment yield faithfully records up stream sediment production in this small 66 km 2 and heavily gla cierized basin implying an effective subglacial erosion rate of 1 6 mm yr these data show that estimates of total yield based upon suspended sediment alone are subject to large errors and suggest that quarrying accounts for a large fraction of the glacial erosion in this system

observed latitudinal variations in erosion as a function of glacier dynamics erosion and velocity data from 15 outlet glaciers covering temperate to polar glacier thermal regimes from patagonia to the antarctic peninsula reveal that over the past century the basin averaged erosion rates vary by three orders of magnitude as a function of climate across this latitudinal transect glacial erosion plays an important role in shaping the earth s landscape but attempts to quantify the long term effect of the erosion of glaciers have proven inclusive and contradictory glacial erosion rates are expected to decrease towards the poles where lower temperatures limit meltwater production thereby reducing glacial sliding erosion and sediment transfer this study presents erosion and velocity data from 15 outlet glaciers covering temperate to polar glacier thermal regimes from patagonia to the antarctic peninsula the dataset reveals that during the past century the basin averaged erosion rates vary by three orders of magnitude as a function of climate across this latitudinal transect the authors suggest that climate and the glacier thermal regime exert more control over erosion rates than the extent of ice cover ice flux or sliding speeds glacial erosion is fundamental to our understanding of the role of cenozoic era climate change in the development of topography worldwide yet the factors that control the rate of erosion by ice remain poorly understood in many tectonically active mountain ranges glaciers have been inferred to be highly erosive and conditions of glaciation are used to explain both the marked relief typical of alpine settings and the limit on mountain heights above the snowline that is the glacial buzzsaw1 in other high latitude regions glacial erosion is presumed to be minimal where a mantle of cold ice effectively protects landscapes from erosion2 3 4 glacial erosion rates are expected to increase with decreasing latitude owing to the climatic control on basal temperature and the production of meltwater which promotes glacial sliding erosion and sediment transfer this relationship between climate glacier dynamics and erosion rate is the focus of recent numerical modelling5 6 7 8 yet it is qualitative and lacks an empirical database here we present a comprehensive data set that permits explicit examination of the factors controlling glacier erosion across climatic regimes we report contemporary ice fluxes sliding speeds and erosion rates inferred from sediment yields from 15 outlet glaciers spanning 19 degrees of latitude from patagonia to the antarctic peninsula although this broad region has a relatively uniform tectonic and geologic history the thermal regimes of its glaciers range from temperate to polar we find that basin averaged erosion rates vary by three orders of magnitude over this latitudinal transect our findings imply that climate and the glacier thermal regime control erosion rates more than do extent of ice cover ice flux or sliding speeds

modeling channelized and distributed subglacial drainage in two dimensions 1 we present a two dimensional glacier drainage system model glads that couples distributed and channelized subglacial water flow distributed flow occurs through linked cavities that are represented as a continuous water sheet of variable thickness channelized flow occurs through rothlisberger channels that can form on any of the edges of a prescribed unstructured network of potential channels water storage is accounted for in an englacial aquifer and in moulins which also act as point sources of water to the subglacial system solutions are presented for a synthetic topography designed to mimic an ice sheet margin for low discharge all the flow is accommodated in the sheet whereas for sufficiently high discharge the model exhibits a channelization instability which leads to the formation of a self organized channel system the random orientation of the network edges allows the channel system geometry to be relatively unbiased in contrast to previous structured grid based models under steady conditions the model supports the classical view of the subglacial drainage system with low pressure regions forming around the channels under diurnally varying input water flows in and out of the channels and a rather complex spatiotemporal pattern of water pressures is predicted we explore the effects of parameter variations on the channel system topology and mean effective pressure the model is then applied to a mountain glacier and forced with meltwater calculated by a temperature index model the results are broadly consistent with our current understanding of the glacier drainage system and demonstrate the applicability of the model to real settings

a comprehensive review on the geomechanical properties of gas hydrate bearing sediments abstract natural gas hydrates ngh that form in sediments beneath the ocean beds are a potential source to meet growing global energy demand gas hydrate bearing sediments ghbs exhibit improved geomechanical properties viz shear strength stiffness compressibility and poisson s ratio that are responsible for their greater stability as compared to the native sediments however dissociation of gas hydrates during extraction of gas instability in the ghbs could trigger submarine slope failures seabed subsidence and failure of the foundations of seafloor installations in order to reduce the risk of occurrence of such geohazards it is imperative to ascertain the stability of ghbs by understanding the variations in their geomechanical properties through field and laboratory investigations which are time consuming and prohibitively expensive for many researchers with this in view the present study attempts to decipher the variation of geomechanical properties with respect to various parameters that affect them viz hydrate saturation sh hydrate morphology and confining pressure temperature conditions by critically synthesizing the existing data in the literature it has been noticed that the shear strength and stiffness are the major parameters influencing the stability of ghbs and both share power law relationship with sh further it is noticed that the cohesion is the predominant component of the shear strength of ghbs and shows significant improvement for sh values greater than 15 50 the variability of cohesion and stiffness with respect to sh have been analysed in tandem with the volumetric deformation during the shearing process to propose particle level mechanism hypothesis that provides an insight in to the stress strain behavior of ghbs the proposed relationships and mechanisms would aid in understanding the behavior and development of improved modeling of geomechanical properties of ghbs

increased channelization of subglacial drainage during deglaciation of the laurentide ice sheet the configuration of subglacial meltwater is a critical control on ice sheet dynamics and the presence of pressurized water distributed across the bed can induce dynamic instabilities however this process can be offset by efficient evacuation of water within large subglacial channels and drainage systems beneath alpine glaciers have been shown to become increasingly channelized throughout the melt season in response to the increased production of meltwater this seasonal evolution has recently been inferred beneath outlet glaciers of the greenland ice sheet but the extent to which this process occurs across much larger spatial and temporal scales is largely unknown introducing considerable uncertainty about the evolution of subglacial drainage networks at the ice sheet scale and associated ice sheet dynamics this paper uses an unprecedented data set of over 20 000 eskers to reconstruct the evolution of channelized meltwater systems during the final deglaciation of the laurentide ice sheet 13 7 kyr b p we demonstrate that eskers become more frequent during deglaciation and that this coincides with periods of increased rates of ice margin recession and climatic warming such behavior is reminiscent of the seasonal evolution of drainage systems observed in smaller glaciers and implies that channelized drainage became increasingly important during deglaciation an important corollary is that the area of the bed subjected to a less efficient pressurized drainage system decreased which may have precluded dynamic instabilities such as surging or ice streaming

micromorphological and geochemical investigation of formation processes in the refectory at the castle of margat qal at al marqab syria margat castle located on the eastern coast of syria is an outstanding example of architecture from the crusader period and the most important castle of the hospitallers who were one of the most famous christian military orders during the medieval period excavations by the syro hungarian archaeological mission have been conducted with the aim of better understanding the history and material culture of this important part of syrian heritage whilst large scale excavation and architectural analysis can provide an understanding of broad changes over the lifetime of the monument high resolution studies of deposits are essential to understand their formation processes and to test hypotheses suggested during excavation in the refectory at margat a series of dark deposits overlain by a pale ashy layer were hypothesised to be the result of a large scale burning event in this study we aimed to test this hypothesis by conducting micromorphological and geochemical analysis of the sequence the first application of microarchaeological techniques to medieval deposits in syria it was observed that the composition of the deposits relates to degradation of anthropogenic debris and constructional material through cycles of wetting drying and microbial and faunal activity rather than fire destruction debris these observations have clarified important changes in the castles function associated with multiple phases of ownership

thermal instability of gas hydrate bearing sediments some issues abstract the overall stability of marine strata holding gas hydrates is dependent on their shear strength characteristics these characteristics in turn are dependent on thermal flux that is imposed for dissociation of the hydrates for the safe and efficient extraction of methane gas from the hydrate bearing sediments due to the imposition of thermal flux on these sediments their fabric structure and pore space hydrate saturation changes which impacts the overall stability of the sea bed estimating stability conditions in such a multiphase and dynamic system necessitates collection of undisturbed samples without compromising their in situ thermodynamic conditions this is a daunting task given the huge cost of procuring samples and the challenge of maintaining an undisturbed sample with in situ thermodynamic conditions till it is brought to the laboratory synthesizing hydrate bearing sample sediments in laboratory for conducting studies to identify heat migration mechanisms and thermal property measurements and linking them to the shear strength characteristics provides an affordable solution to this problem with this in view a critical review of the available literature dealing with laboratory synthesis of hydrate bearing sediments their thermal and strength characteristics the coupled phenomenon of heat and fluid migration and its impact on the overall stability of marine sediments has been conducted and presented in this paper this will facilitate understanding the factors governing and the mechanism of heat transfer in a multiphase system the changes in the system brought about by the hydrate dissociation front and the overall impact on the stability of seabed

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

the sediment budget of an alpine cirque cirques form and evolve as glaciers attack the bed and subaerial processes dismantle the surrounding walls collectively these processes which can make a cirque longer or deeper or both profoundly influence near divide regions of glaciated mountains and yet are rarely studied in a systematic way toward this end we developed a theoretical framework for the sediment budget of a cirque that includes sediment sources transport pathways and storage elements we quantified each component of the sediment budget using field measurements and remote sensing data of a glaciated alpine cirque in british columbia canada the cirque has a plan view area of 1 64 km 2 and relief of 780 m our budget values which correspond to a period of substantial glacier retreat are based on measurements reflecting time intervals ranging from 1 yr to 80 yr we report errors as a range enclosed in parentheses analogous to 95 confidence bounds on average 1640 250 7950 metric tons of rock are released by the headwall each year nearly 90 of this debris leaves the wall as small rockfalls or in snow avalanches our field observations indicated that snow avalanches originating as cornice failures are currently the most important transport process on the headwall we estimated the mass of debris transported annually by the glacier to the foreland using 1 the volume and age of the foreland ground moraine and 2 the product of rock mass per unit volume of ice and glacier velocity over the past several decades the glacier delivered 6440 1180 14930 tons yr to the foreland via forward ice motion and margin retreat mostly in subglacial till or sediment rich basal layers less than 3 of the glacierborne sediment flux traveled as supraglacial debris 170 50 320 tons yr at present sediment evacuation from the cirque occurs in a single meltwater stream we monitored water discharge and suspended sediment concentration in this stream between 29 june and 28 august 2007 by season s end 650 80 1860 tons of sediment had passed our gauging station equivalent to an erosion rate of 0 2 0 03 0 70 mm yr when averaged over the glacier bed approximately one third of the total annual streamborne sediment transport occurred over a 2 d period during the first major melt event of the year using our budget relations and flux magnitudes we estimate the glacier is removing between 1240 and 2470 tons of rock from its bed per year a rate equivalent to 0 5 0 9 mm yr of erosion glacierwide the headwall by comparison is being worn away horizontally at 1 2 0 2 5 9 mm yr thus our results suggest that the headwall is retreating at rates roughly equivalent to vertical incision by the glacier our sediment budget results demonstrate that the wide variety of sediment sources and transport processes active in cirques necessitates a holistic view of cirque formation one that most morphometric range scale and glacial erosion analyses ignore

pollen analysis of core ds7 1sc dead sea showing intertwined effects of climatic change and human activities in the late holocene the dead sea sediment holds the archives of a complex relationship between ever changing nature and ancient civilisations here the detailed pollen analyses of core ds7 1sc off ein gedi are presented for the first time the record covers the last 2500 years the facies changes from halite when no freshwater flows in the dead sea to laminites when rainfall provides sufficient inflow for the jordan and subsidiary rivers a couple of times through the record the pollen diagram supported by the facies change shows a wetter roman byzantine period which allowed intensive arboriculture and a wetter period at the end of the xixth and beginning of the xxth centuries the latter in good relation with historical and instrumental data based on radiocarbon chronologies on several pollen diagrams along the western dead sea shore the transition to drier climates and the transition to pastoralism are suggested to take place between a few decades before the islamic period and close to this transition a high resolution palynological study of the individual laminae forming the laminites aragonite and gypsum in the summer versus detritics in winter confirms the seasonal character of the laminae but throws a note of caution as for their regular annual character

rapid erosion beneath the greenland ice sheet the pleistocene ice sheets left a clear signature of erosion but the rate at which ice sheets erode is difficult to determine from either paleolandscapes or observations of contemporary processes here we use two years of sediment flux data derived from meltwaters emerging from an outlet glacier in west greenland to calculate an average rate of subglacial erosion across a catchment extending 50 km inland from the ice margin erosion in this zone occurs at 4 8 2 6 mm a 1 a rate 1 2 orders of magnitude greater than previous estimates of erosion rate beneath the greenland ice sheet our results suggest that where surface meltwaters are able to access the bed the rate of erosion by ice sheets is in keeping with the rapid erosion observed at temperate alpine glaciers during deglacial phases when meltwater was abundant ice sheet margins should therefore have acted as highly efficient agents of erosion

regional synthesis of mediterranean atmospheric circulation during the last glacial maximum atmospheric circulation leaves few direct traces in the geological record making reconstructions of this crucial element of the climate system inherently difficult we produced a regional mediterranean synthesis of paleo proxy data from the sea surface to alpine altitudes this provides a detailed observational context for change in the three dimensional structure of atmospheric circulation between the last glacial maximum lgm 23 000 to 19 000 years ago and the present the synthesis reveals evidence for frequent cold polar air incursions topographically channeled into the northwestern mediterranean anomalously steep vertical temperature gradients in the central mediterranean imply local convective precipitation we find the lgm patterns to be analogous though amplified to previously reconstructed phases of enhanced meridional winter circulation during the maunder minimum the little ice age

experimental study of bedrock channel alluviation under varied sediment supply and hydraulic conditions 1 channel incision into bedrock plays a critical role in mountain landscape evolution a bed that is completely alluviated cannot undergo incision as a result incision driven by the collision of bedload grains and bedrock requires transport at below capacity conditions for example where the bed is partially covered by alluvium in a mechanistic model of bedrock incision it is important to have a formula describing the relationship between the bedload transport rate and the degree to which the bed is covered by sediment the purpose of this work is to understand the mechanisms underlying the degree of bed exposure in bedrock rivers by means of an experimental study a number of experiments with various hydraulic and morphological bed conditions were performed in order to characterize this model here we focus on planar bedrock beds with some roughness the results suggest that the sediment supply channel slope hydraulic bed roughness the degree of areal coverage and thickness of antecedent gravel in the channel as well as the presence of boulders in the channel are major factors controlling bedrock exposure for sufficiently low ratios of sediment supply to transport capacity it was found that bedrock roughness can play a role in determining the degree of bedrock exposure for higher sediment ratios on the other hand the composite roughness associated with grain roughness bars and or antidunes dominates so that the underlying bedrock roughness no longer affects the degree of exposure of the bed for lower bed slopes i e less than 0 015 based on our experimental setting bedrock exposure decreases more or less linearly with increasing values of the ratio of sediment supply rate to capacity rate for higher bed slopes i e more than 0 015 there is a range of lower values of the ratio of sediment supply rate to capacity rate where a bedrock surface becomes fully exposed without any alluvial deposit for a given bedrock roughness this range expands solely with increasing slope regardless of shear stress within the upper range of values of the ratio of sediment supply to capacity rate a linear relationship between the degree of bedrock exposure and this supply to capacity ratio still prevails the addition of model boulders can be viewed as very high hydraulic bed roughness to the channel has been found to suppress the overexposure of bedrock and so restore a linear relation between the degree of exposure and the ratio of sediment supply rate to capacity rate formulations for estimating bedrock exposure as a function of sediment supply to capacity ratio under different river channel characteristics are proposed a linear relation between the degree of alluvial cover and the ratio of sediment supply rate to capacity rate is a previously proposed model the present study expands the result for other cases including runaway alluviation some landscape evolution models assume an abrupt shift between fully exposed bedrock and complete alluviation whereas others assume the linear relation the present study shows that both formulations are valid under different settings of river characteristics

critical state soil constitutive model for methane hydrate soil 1 this paper presents a new constitutive model that simulates the mechanical behavior of methane hydrate bearing soil based on the concept of critical state soil mechanics referred to as the methane hydrate critical state mhcs model methane hydrate bearing soil is under certain geological conditions known to exhibit greater stiffness strength and dilatancy which are often observed in dense soils and also in bonded soils such as cemented soil and unsaturated soil those soils tend to show greater resistance to compressive deformation but the tendency disappears when the soil is excessively compressed or the bonds are destroyed due to shearing the proposed model represents these features by introducing five extra model parameters to the conventional critical state model it is found that for an accurate prediction of ground settlement volumetric yielding plays an important role when hydrate soil undergoes a significant change in effective stresses and hydrate saturation which are expected during depressurization for methane gas recovery

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

proglacial erosion rates and processes in a glacierized catchment in the swiss alps in the swiss alps climatic changes have not only caused glacier retreat but also likely increased sedimentation downstream of glaciers this material either originates from below the glacier or from periglacial environments exposed as glaciers retreat and often consist of easily erodible sediment griesgletscher s catchment in the swiss alps was examined to quantify erosion in theproglacial area possible hydrological drivers and contributions of the sub and periglacial sources digital elevation models created from annual aerial photographs were subtracted to determine annual volume changes in the proglacial area from 1986 to 2014 these data show a strong increase in proglacial erosion in the decade prior to 2012 coincident with increasing proglacial area size however examination of the gradient between discharge and sediment evacuation and the modeled sediment transport could suggest that the proglacial area began to stabilize and sediment supply is limited the large influx of sediment into the proglacial reservoir which is roughly 2 5 times greater than the amount of sediment eroded from the proglacial area demonstrates the importance of subglacial erosion to the catchment s sediment budget although far more sediment originates subglacially erosion rates in the proglacial area are over 50 times greater than the rest of the catchment in turn both sub and periglacial processes in addition to constraining sediment supply must be considered forassessing future sediment dynamics as glacier area shrinks and proglacial areas grow

late holocene 0 2 4 ka bp surface water temperature and salinity variability feni drift ne atlantic ocean abstract planktonic foraminiferal mg ca ratios and oxygen isotopic compositions of a spliced sediment record from feni drift ne atlantic ocean box core m200309 and piston core enam9606 trace late holocene sea surface temperature sst and salinity changes over the past 2400 years at this location the variability of sst and oxygen isotopic composition of seawater 18 o w reflects variable northward advection of warm and saline surface waters which appears linked to climate variability over the adjacent european continent our records reveal a general long term cooling trend superimposed on this overall trend partly higher temperatures and salinities from 180 to 560 ad and 750 to 1160 ad may be ascribed to the roman and medieval warm periods respectively subsequently our record displays highly variable surface water conditions the main little ice age sst minimum is restricted to the 15th and 16th centuries ad pervasive multidecadal to centennial scale variability throughout the sedimentary proxy records can be partly attributed to solar forcing and or variable heat extraction from the surface ocean caused by shifts in the prevailing state of the north atlantic oscillation nao high salinities in the 17th and 18th centuries are considered to reflect tropical anomalies linked to a southward shift of the intertropical convergence zone propagating across the north atlantic ocean

evolution of subglacial overdeepenings in response to sediment redistribution and glaciohydraulic supercooling received 16 august 2012 revised 18 december 2012 accepted 15 january 2013 1 glaciers erode bedrock rapidly but evacuation of sediments requires efficient subglacial drainage networks if glaciers erode more rapidly than evacuation proceeds a protective subglacial till layer can form to armor the bed where glaciers cross overdeepenings local closed depressions the bed slope opposes the ice surface and lowers the hydraulic potential gradient that drives water flow here we present results of a dynamic distributed model of coupled basal water flow and sediment transport to show how overdeepenings evolve over the course of a melt season we use steady state calculations as well as numerical simulations to understand how alluvial bed erosion alters overdeepenings numerical results from a modified form of the spring hutter equations show behaviors that cannot be inferred from either local or steady state calculations in general opposition of surface and bed slopes lessens sediment transport regardless of ice accretion from glaciohydraulic supercooling drainage efficiency strongly affects erosion and deposition rates results show characteristic behaviors of flow through overdeepenings such as overpressured water systems and accretion rates compatible with field measurements simulations that start with overdeepened glacier configurations progress out of a freezing regime where glaciohydraulic supercooling occurs this progression indicates that glacier hydrology is more strongly affected by erosion and deposition than by freezing from glaciohydraulic supercooling we discuss how this outcome affects glacier erosion and sediment transport under modern and past ice sheets

influence of rapid glacial retreat on the rate of erosion by tidewater glaciers glacial erosion rates inferred from total sediment budgets in recently deglaciated fjords which are the highest reported erosion rates worldwide have received considerable attention in fields as diverse as tectonics glacial sedimentation and climate these record rates however are representative only of tidewater glaciers during their extensive retreat of the post little ice age period erosion rates averaged over glacial interglacial cycles and longer periods are likely to be substantially smaller we examine the influence of retreat rate on sediment yields from tidewater glaciers by reconstructing the history of sediment output from retreating glaciers necessary to produce sediment packages observed in contemporary fjords using a simple numerical model of proglacial sedimentation in front of a retreating glacier seismic profiles of proglacial sediments and the history of terminus retreat of muir glacier glacier bay alaska we calculate the sediment flux as a function of time from this glacier between 1900 and 1979 and conclude that sediment flux scales with retreat rate the corresponding basin wide erosion rate during this 79 yr period averages 37 mm yr and exceeds long term erosion rates by a factor of 5 1 for muir glacier and by inference for other calving glaciers the general drastic retreat and the marked regional drawdown of ice since the little ice age are both linked to unusually rapid calving and fast ice motion which is conducive to rapid erosion

buried and open tunnel valleys in denmark erosion beneath multiple ice sheets abstract tunnel valleys are large elongate and irregular depressions cut beneath the margin of former ice sheets they are generally believed to play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour their origin however remains poorly understood examination of newly collected danish hydrogeophysical and lithological data has revealed numerous systems of buried valleys 50 350 m deep and 0 5 4 km wide these valleys are similar to the open tunnel valleys found in the present day landscape infills comprise a variety of sediments often with subglacial clay till and meltwater deposits the incised substratum consists of limestone heavy paleogene clay sand and silt the tunnel valleys have preferred orientations and can be divided into several generations each ascribed individual ice advances or ice sheets occurring during multiple glaciations the processes forming the valleys appear to prefer pre existing open and buried valleys for the renewed erosion thus old subglacial erosion pathways have been re used several times and some of the present tunnel valleys may have been established in the middle or early quaternary or even earlier this valley re use effect causes apparently anastomosed valley systems to emerge in the data images the valleys were mainly eroded by meltwater supposed to have drained from subglacially stored reservoirs probably behind a frozen margin the water was most likely released in repeated jokulhlaups and flowed in relatively small channels on the floors of the tunnel valleys which gradually became ice filled with the lowering of the bed selective linear glacial erosion is also believed to have contributed to the erosion this however was most pronounced for the widest valleys and is supposed to have played a secondary role

erosion rates during rapid deglaciation in icy bay alaska 1 contemporary glacial erosion rates based on sediment yields in southeast alaska merit considerable attention because they are unsurpassed worldwide and they significantly exceed long term exhumation rates in the region two issues are likely to contribute to these high rates contemporary sediment yields in fjords 1 have generally been overestimated by failing to account for the considerable input of subaerially derived material and 2 are exceptionally high because tidewater glaciers in southeast alaska have been anomalously dynamic and erosive during the past century of rapid retreat to investigate these influences and to quantify the rate at which tyndall glacier erodes its basin we present seismic data defining the volume of sediments in taan fjord icy bay we subtract the contribution of subaerially derived sediments from the fjord sediment package to determine the sediment yield directly from tyndall glacier during the most recent period of retreat 1962 1999 using a numerical model of proglacial glacimarine sedimentation we then calculate the annual sediment yield from and the corresponding erosion rate of tyndall glacier during this period which averages 28 5 mma 1 a strong correlation emerges between glacial retreat rates and glacial sediment yields implying that most contemporary sediment yield data from retreating tidewater glaciers may correspond to contemporary erosion rates that are a factor of 3 5 1 5 higher than in the long term hence we estimate the long term erosion rate for tyndall glacier to be 9 2 mma 1

triaxial compressive properties of artificial methane hydrate bearing sediment 1 knowledge of the mechanical properties of gas hydrate bearing sediments is essential for simulating the geomechanical response to gas extraction from a gas hydrate reservoir in this study drained triaxial compression tests were conducted on artificial methane hydrate bearing sediment samples under hydrate stable temperature pressure conditions toyoura sand average particle size d50 0 230 mm number 7 silica sand d50 0 205 mm and number 8 silica sand d50 0 130 mm were used as the skeleton of each specimen axial loading was conducted at an axial strain rate of 0 1 min 1 at a constant temperature of 278 k the cell and pore pressures were kept constant during axial loading we found that the strength and stiffness of the hydrate sand specimens increased with methane hydrate saturation and with the effective confining pressure and the secant poisson s ratio decreased with the effective confining pressure the stiffness depends on the type of sand forming the skeleton of the specimens although the strength has little dependence on the type of sand according to an earlier work hydrate sand specimens are thought to contract in the early stage of axial loading before starting to expand owing to the dilatancy effect as is the case for many other geological materials the test results in this study are discussed in relation to the deformation mechanism proposed in an earlier work

transient subglacial hydrology of a thin ice sheet insights from the chasm esker british columbia canada abstract glacier drainage systems are never steady state instead they fluctuate over time and space in response to variation in water input in order to improve numerical models of glacier hydrology it is important to fully understand the processes controlling subglacial drainage system evolution but contemporary ice sheet beds are typically inaccessible thus esker distribution morphology and sedimentology have been used to infer the dynamics and hydrology of former ice sheets however debate remains as to the processes responsible for esker formation and most theoretical investigations have assumed that they formed due to processes that operated beneath thick ice despite many field investigations to the contrary we investigate esker formation during the final stages of the thin inactive and rapidly decaying cordilleran ice sheet cis in interior british columbia canada a combination of geomorphological ground penetrating radar gpr and electrical resistivity tomography ert data suggest esker ridge sedimentary architecture is consistent with synchronous formation during a glacial lake outburst flood glof these data reveal esker ridge deposition most likely took place within an ice tunnel that evacuated late waning stage flow following erosion and partial fill of a broader meltwater corridor esker ridge sedimentary architecture reveals this depositional environment was dynamic reflecting complex interaction between ice thickness ice structure ice tunnel geometry flow conditions and sediment supply under these thin inactive ice conditions ice tunnel location was initially governed by structural weaknesses in the ice and or equipotential gradient because creep closure rates were low the ice tunnel evolved through feedbacks between conduit growth via frictional melting mechanical ice excavation and conduit closure due to sediment infilling rather than ice creep this resulted in a non uniform ice tunnel that enlarged in an upglacier direction and locally unroofed to form open channels during its final stages these data suggest that eskers may record unsteady rather than steady flows in a drainage network and so the assumptions often made when using eskers to inform hydrological components of ice sheet models may not be applicable to all ice sheet settings

study on the mechanical properties of hydrate bearing silty clay the mechanical properties are important for the evaluation of stratum deformation and instability in hydrate exploitation by using an integrated test apparatus for synthesis of hydrate sediment and triaxial tests a series of compression tests is conducted on the silty clay containing tetrahydrofuran hydrate scth similar to that of south china sea the stress strain curves and mohr circles are obtained at different degree of hydrate saturations and confining pressures the silty clay containing tetrahydrofuran hydrate shows typical ductile behavior the shear strength increases linearly with the increase of hydrate saturation and confining pressure the secant modulus increases with the increase of hydrate saturation the shear strength is analyzed based on the drucker prager criterion mohr coulomb criterion lade duncan criterion while the secant modulus is analyzed using the mixed law of composite materials it is shown that the strength can be well described by the drucker prager criterion and mohr coulomb criterion and the secant modulus is close to the harmonic average of the modulus of soil skeleton and hydrate in scth c 2015 elsevier ltd all rights reserved

medieval coastal syrian vegetation patterns in the principality of antioch the coastal area of jableh in the vicinity of the saladin and al marquab castles is a fertile alluvial plain located on the northwestern part of syria in what was once the crusader principality of antioch in order to detail the coastal environment during the crusader period in the middle east palynological analyses have been conducted on the underlying coastal alluvial deposits the recovered sediments represent a continuous record of the environmental history of the area spanning a c ad 850 1850 cal yr period from the muslim era up to and including the late ottoman times during the local crusader period ad 1100 1270 the area was dominated by an arborescent mattoral mixed with a xerophytic shrub steppe the alluvial plain was slightly waterlogged and colonized by a wetland meadow with an open vegetation of steppe like character on bare surfaces and fresh arable soils the riparian and open deciduous riverine forests were weakly developed signs of agricultural activities are mainly recorded for the high medieval period ad 1000 1300 with an increase of vineyards in the coastal area since c ad 1250 cal yr until the end of the crusader period agricultural activities never reached the same intensity as during the mameluke sultanate and the ottoman empire

holocene environmental change in southwest turkey a palaeoecological record of lake and catchment related changes percentage concentration and accumulation pollen data together with diatom and non siliceous microfossil data are presented for the site of go lhisar go l u 37i8 n 29i36 e elevation 930 m a small intramontane lake in burdur province southwest turkey microfossil assemblages from the longest sediment core gha 813 cm record changes in local and regional vegetation and lake productivity over the last 9500 years pollen spectra indicate that vegetation progressed from an open landscape with an increase in arboreal pollen occurring 8500 bp to mixed forest comprising oak pine and juniper until around 3000 bp cal 1240 bc when a human occupation phase becomes discernible from the pollen spectra this occurs shortly after the deposition of a volcanic tephra layer which originated from the minoan eruption of santorini thera and radiocarbon dated to 3330 70 yr bp cal 1600 bc this human occupation phase is comparable to the beys ehir occupation phase recorded at other sites in southwest turkey and involved forest clearance and the cultivation of fruit trees such as olea juglans castanea and itis together with arable cereal growing and pastoralism the presence of pollen types associated with the beys ehir occupation phase in deposits above the santorini tephra layer confirms a late bronze age early anatolian dark age date for its commencement since 3000 bp notable changes in aquatic ecology associated with tephra deposition and subsequent nutrient and sediment flux from the lake catchment are recorded the beys ehir occupation phase at go lhisar go l u came to an end around 1300 bp cla ad 700 when pine appears to have become the dominant forest tree 1999 elsevier science ltd all rights reserved

integrated hydrologic and hydrochemical observations of hidden creek lake jokulhlaups kennicott glacier alaska 1 hidden creek lake hcl an ice marginal lake impounded by kennicott glacier wrangell mountains alaska fills annually to 20 to 30 106 m3 and then drains subglacially within 2 to 3 days during the 1999 and 2000 jokulhlaups we carried out a series of planned observations around the lake and in the kennicott river which drains the glacier approximately 20 of the lake volume was contained within a subglacial water wedge beneath the ice dam the entire volume of the lake drains through the wedge hydraulic head loss through this constriction may be responsible for the fairly symmetrical shape of the hcl outflow hydrographs deduced from lake level records basin hypsometry and collapse of the ice dam the flood hydrographs in the kennicott river are similar in shape to the outflow hydrographs and within error lake volume matched the river flood volume in both years up to 12 106 m3 of water was temporarily stored within the glacier during the 2000 jokulhlaup during the 2000 jokulhlaup the background flow in the kennicott river shifted to a dilute chemical composition as the hcl jokulhlaup progressed donoho falls lake filled with water whose chemistry was closer to that of the background flow in kennicott river than to hcl water comparison of these chemical signals with typical summer variations in kennicott river chemistry suggests that the jokulhlaup created high subglacial water pressure that impeded normal drainage of solute rich water from a distributed drainage system into a conduit system at the glacier bed and even caused flow direction locally to reverse

deglacial meltwater drainage and glaciodynamics inferences from laurentide eskers canada abstract this paper evaluates current knowledge of laurentide eskers in canada in the light of developments in glacier hydrology and glacial sedimentology questions regarding the morpho sedimentary relations of eskers the synchroneity and operation of r channel systems the role of supraglacial meltwater input and proglacial water bodies the controls on esker pattern and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed a morphologic classification of eskers is proposed five types of eskers are identified and investigated type i eskers likely formed in extensive synchronous dendritic r channel networks under regionally stagnant ice that terminated in standing water type ii eskers likely formed in short subaqueously terminating r channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation type iii eskers plausibly formed in short r channels that drained either to interior lakes in or tunnel channels under regionally stagnant ice type iv eskers may have formed as time transgressive segments in short subaerially terminating r channels or reentrants that developed close to the ice margin as the ice front underwent stagnation zone retreat or downwasted and backwasted regionally stagnant ice however formation in synchronous r channels cannot be discounted on the basis of reported observations type v eskers may have formed in h channels that terminated subaerially the spatial distribution of these esker types is discussed the factors that determined laurentide r channel pattern and operation were likely a complex combination of i supraglacial meltwater discharge ii the number and location of sink holes iii the ice surface slope thickness and velocity and iv the permeability topography and rigidity of the bed these factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle

the role of sediment supply in esker formation and ice tunnel evolution abstract meltwater is an important part of the glacier system as it can directly influence ice sheet dynamics although it is important that ice sheet models incorporate accurate information about subglacial meltwater processes the relative inaccessibility of contemporary ice sheet beds makes direct investigation challenging former ice sheet beds contain a wealth of meltwater landforms such as eskers that if accurately interpreted can provide detailed insight into the hydrology of former ice sheets eskers are the casts of ice walled channels and are a common landform within the footprint of the last laurentide and cordilleran ice sheets in south western alberta esker distribution suggests that both water and sediment supply may have been important controls the longest esker ridge segments are located within meltwater valleys partially filled by glaciofluvial sediments whereas the shortest esker ridge segments are located in areas dominated by clast poor till through detailed esker ridge planform and crest type mapping and near surface geophysics we reveal morpho sedimentary relationships that suggest esker sedimentation was dynamic but that esker distribution and architecture were primarily governed by sediment supply through comparison of these data with data from eskers elsewhere we suggest three formative scenarios 1 where sediment supply and flow powers were high coarse sediment loads result in rapid deposition and rates of thermo mechanical ice tunnel growth is exceeded by the rate of ice tunnel closure due to sediment infilling high sedimentation rates reduce ice tunnel cross sectional area cause an increase in meltwater flow velocity and force ice tunnel growth thus ice tunnel growth is fastest where sedimentation rate is highest this positive feedback results in a non uniform ice tunnel geometry and favours macroform development and non uniform ridge geometry 2 where sediment supply is limited but flow power high the rate of sedimentation is less than the rate of thermo mechanical ice tunnel growth here the ice tunnel enlarges faster than it fills with sediment and its evolution is independent of sedimentation resulting in more uniform ice tunnel geometry in these cases esker architecture is dominated by extensive vertical accretion of tabular units and ridge geometry is more uniform 3 where sediment is truly supply limited the sedimentation rate is negligible regardless of water supply and like scenario 2 ice tunnel growth is independent of sediment deposition forming a relatively uniform ice tunnel or eroding the bed because meltwater flows transport few gravel clasts the ice tunnel is not completely filled with gravel and instead saturated and pressurized diamicton or bedrock if deformable from beneath the surrounding ice is squeezed into the relatively low pressure ice tunnel during waning flow or after ice tunnel shutdown resulting in deformation of limited gravels deposited within the ice tunnel and a landform cored with diamicton or deformed bedrock and with a relatively uniform ridge geometry our data demonstrate that an esker map is a minimum map of ice walled channel location and that continued detailed investigation of morpho sedimentary relationships is essential to gaining a complete picture of esker forming processes validating the morpho sedimentary relationships identified in south western alberta and other areas with a larger data set may allow improved remote predictive esker mapping over larger areas and inferences to be made about spatial and temporal variations in esker depositional environments and ice tunnel evolution

links between proglacial stream suspended sediment dynamics glacier hydrology and glacier motion at midtdalsbreen norway two hourly suspended sediment concentration variations observed during the summer of 1987 in the proglacial stream draining midtdalsbreen norway are modelled using multiple regression and time series techniques suspended sediment fluctuations are influenced by stream discharge variations diurnal hysteresis effects medium term sediment supply and transport variations and the recent suspended sediment concentration history of the stream they do not appear to be influenced by seasonal exhaustion or rainfall variations possible reasons for this are discussed large positive residuals from the fitted models are major pulses of suspended sediment unrelated to discharge variations these sediment flushes correlate with periods of enhanced glacier motion they cannot be explained by enhanced sediment production by subglacial erosion but are probably due to the tapping of subglacially stored sediment during sudden changes in the hydraulics and or configuration of the subglacial hydrological system seasonal changes in the lag between glacier motion peaks and suspended sediment flushes suggest that the subglacial hydrological system evolves over the summer from a distributed to a more channelized configuration

bedload hysteresis in a glacier fed mountain river sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before counterclockwise hysteresis or after clockwise hysteresis the peak of bedload hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions respectively hysteresis has been mainly explored for the case of suspended sediment transport but it was rarely reported for bedload transport in mountain streams this work focuses on the temporal variability of bedload transport in an alpine catchment saldur basin 18 6 km2 italian alps where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0 5m long steel pipe runoff dynamics are dominated by snowmelt in late spring early summer mostly by glacier melt in late summer early autumn and by a combination of the snow and glacier melt in mid summer the results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin on the contrary counterclockwise hysteresis tend to be more frequent during late glacier melting period possibly due to the time lag needed for sediment provided by the glacial and peri glacial area to be transported to the monitoring section however intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis thus indicating the activation of different sediment sources these results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams

modeling sediment transport in ice walled subglacial channels and its implications for esker formation and proglacial sediment yields sediment yields from glacierized basins are used to quantify erosion rates on seasonal to decadal timescales as well as conditions at the glacier bed and eskers hold valuable information about past subglacial hydraulic conditions in their spatial organization geometry and sedimentary structures ultimately eskers are a record of past glacio fluvial sediment transport but there is currently no physical model for this process we develop a 1 d model of morphodynamics in semicircular bedrock floored subglacial channels we adapt a sediment conservation law developed for mixed alluvial bedrock conditions to subglacial channels channel evolution is a function of melt opening by viscous heat dissipation from flowing water and creep closure of the overlying ice to which we add the closure or enlargement due to sediment deposition or removal respectively we apply the model to an idealized land terminating glacier and find that temporary sediment accumulation in the vicinity of the terminus or the formation of an incipient esker is inherent to the dynamics of the channelized water flow the alluviation of the bed combined with the pressurized channel flow produces unexpected patterns of sediment evacuation we show that the direction of hysteresis between sediment and water discharge is not necessarily linked to a supply or transport limited system as has been hypothesized for proglacial sediment yields we also find that the deposition of an incipient esker is a function of a compromise between water discharge and sediment supply but perhaps more importantly ice surface slope and the temporal pattern of water delivery to the bed

substantial export of suspended sediment to the global oceans from glacial erosion in greenland approximately 8 of the fluvial suspended sediment exported to the world s oceans comes from rivers draining the greenland ice sheet according to an analysis of satellite imagery furthermore the export is dominated by areas where subglacial erosion is high