jokulhlaups a reassessment of floodwater flow through glaciers 1 in glaciated catchments glacier generated floods jokulhlaups put human activity at risk with large sporadic jokulhlaups accounting for most flood related fatalities and damage to infrastructure in studies of jokulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier however some jokulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage by focusing on icelandic jokulhlaups this article reassesses how floodwater flows through glaciers it is argued that two physically separable classes of jokulhlaup exist and that not all jokulhlaups are an upward extrapolation of processes inherent in events of lesser magnitude and smaller scale the hydraulic coupling of multiple nonlinear components to the flood circuit of a glacier can induce extreme responses including pressure impulses in subglacial drainage representing such complexity in mathematical form should be the basis for upcoming research as future modeling results may help to determine the glaciological processes behind heinrich events moreover such an approach would lead to more accurate predictive models of jokulhlaup timing and intensity

the geomorphology and sedimentology of eskers in north central ireland abstract eskers are common glacial landforms in ireland and form regionally extensive networks that reflect stages of ice retreat of this sector of the late devensian weichselian british irish ice sheet however the sedimentary structures and composition of these eskers are poorly known despite being able to offer valuable insight into subglacial hydrological processes during deglaciation this study presents detailed morphological and sedimentary evidence from six esker systems in north central ireland where adjacent and interacting ice domes were characterized by changes in ice bed thermal and hydrological properties as well as significant ice dome centre migration morphologically esker ridges in this area vary in length size and continuity with some esker systems ascending over hills thus crossing watersheds whereas other systems are confined to basin settings esker systems commonly appear to feed terminal outwash and glaciolacustrine deltas but several systems do not show a clear terminus the internal sediments within eskers vary from concentrically bedded sands and gravels formed within enclosed tunnels to interbedded sands gravels and diamictons occasionally with water induced soft sediment deformations that are likely formed in interlobate settings in contrast with some previous glacier models that assume that esker systems are isochronous and were formed in solely subglacial settings the esker systems described here are interpreted as being of different ages formed in variously subglacial to ice marginal settings and thus cannot be used as a single snapshot of the disposition of ice domes during stages of late devensian ice retreat

new insights into the subglacial and periglacial hydrology of vatnajokull iceland from a distributed physical model we apply a time dependent distributed glaciohydraulic model tovatna jo kull ice cap iceland aiming to determine the large scale subglacial drainage structure theimportance of basallyderivedmeltwater theinfluence ofapermeable glacierbedand vatnajo kull s discharge contribution to major rivers in iceland the model comprisestwo coupled layersthatrepresentthesubglacialhorizonperchedona subsurfaceaquifer inthe western sector and bedrock in the eastern sector to initialize and drive the simulations we use digital elevation models of the ice surface and bed the1999 2000 measured mass balance and an estimate of subglacial geothermal heat fluxes the modelled subglacial flow field differs substantially from that derived by hydraulic potential calculations and the corresponding distribution of basal effective pressure shows a strong correlation between low effective pressure and surge prone areas in northeastern and southern sectors of vatnajo kull simulations suggest that geothermally derived basal melt may account for upto 5 of the annualglacial discharge and buried aquifers may evacuate up to 30 ofsubglacialwater time dependenttestsyieldestimatesoftheglacialdischargecomponent in various outlet rivers and suggest a possible seasonal migration of subglacial hydraulic divides this study of present dayvatnajo kull hydrology formsthe starting point for inves tigationsof its future evolution

age of the pineo ridge system implications for behavior of the laurentide ice sheet in eastern maine u s a during the last deglaciation abstract the laurentide ice sheet was a major driver of global sea level change during the last deglaciation and may have impacted both atmospheric and oceanic circulation an understanding of past changes in the ice sheet is important for constraining its interaction with other components of the climate system here we present the geologic context and chronology for ice sheet fluctuations in eastern maine adjacent to the north atlantic ocean thought to be a key player in the termination of the last ice age retreat of the laurentide ice sheet through coastal maine first produced a series of lobate grounding line moraines followed by deposition of the prominent pineo ridge system which crosscut the earlier moraine set and which is characterized by extensive ice contact deltas closely spaced parallel moraines and association with eskers our new 10 be surface exposure ages indicate that the pineo ridge system which extends for more than 100 km in eastern maine and atlantic canada dates to 15 3 ka 800 years older than recent estimates our data are in accord with inboard minimum limiting radiocarbon ages of terrestrial materials which indicate deglaciation as early as 15 3 ka as well as of marine shells that are as old as 15 0 ka both the deglaciation that produced the lobate moraines and the short lived readvance that led to the pineo ridge system occurred during heinrich stadial 1 given that faunal and isotopic evidence indicates that the ocean remained cold during deglaciation of coastal maine we infer that ice recession was due to rising summer air temperatures that gave way briefly to cooling to allow minor readvance glacial deposits north of the pineo ridge system display evidence of ice stagnation and downwasting suggesting rapid ice retreat following deposition of the delta moraine complex coincident with the onset of the bolling

geomorphic evidence for active and inactive phases of late devensian ice in north central ireland abstract in the clogher valley north central ireland subglacial and proglacial landforms provide evidence for phases of active and inactive subglacial and ice marginal processes during the late devensian weichselian glaciation 22 13 kyr bp patterns of subglacial rogen moraines and drumlins record east to west ice flow along the valley axis during maximal ice stages eskers superimposed upon the rogen moraines and drumlins record later west to east ice flow and mark the first stages of ice retreat areas of large ice marginal non aligned ridges and mounds are separated by more extensive areas in which no deglacial landforms or sediments are present the non aligned ridges and mounds do not show a dominant directional signature have intricate basal outlines steep slopes and high relief

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

an analysis of sinuous ridges in the southern argyre planitia mars using hirise and ctx images and mola data 1 a suite of sinuous ridges with branching and braided morphologies forms an anastomosing network in southern argyre planitia mars several modes of origin have been proposed for the argyre ridges imagery from the high resolution imaging science experiment hirise and context camera ctx aboard mars reconnaissance orbiter mro and mars orbiter laser altimeter mola topographic data sets from mars global surveyor mgs are used to constrain processes involved in formation of the argyre ridges we find the characteristics of the ridges and associated layered deposits consistent with glaciofluvial lacustrine processes and conclude that the ridges are most likely eskers in particular variations in ridge height appear to be related to the surrounding surface slope ridge height increases with descending slopes and decreases with ascending slopes this characteristic is observed in terrestrial eskers and is related to subice flow processes the nature of some eroding beds in the ridges suggests induration if the argyre ridges are indeed eskers the southern argyre basin was once covered by the margin of a large thick stagnating or retreating ice deposit that extended for hundreds of kilometers or more during ridge formation water flowed on top within or beneath the ice deposit the continuity and preservation of the ridges suggests that flow was primarily at the base of the ice the dimensions up to hundreds of meters tall and several kilometers wide aspect ratio and extent hundreds of kilometers of the ridges as well as preliminary calculations of discharge suggest that a significant amount of water was available

pool patterning in a northern peatland geophysical evidence for the role of postglacial landforms a hydrogeophysical study conducted in a 2200 ha peatland in central maine shows evidence that a laterally continuous esker deposit extends below the peat soil following the direction of glacier retreat and coinciding with the presence of a pool system ground penetrating radar gpr electrical resistivity er imaging and terrain conductivity measurements were constrained with limited hydrological measurements direct sampling of inorganic sediments and radiocarbon dating of peat soils to develop a conceptual model for pool formation that could explain the unique pool patterning observed in other northern peatlands gpr profiles revealed three dimensional images of two esker crests below the easternmost edge of the pool area gpr data was supported by er imaging and terrain conductivity data and allowed for facies differentiation to infer processes related to esker formation during the glacier front retreat hydrologic data showed preferential flow of groundwater towards the esker suggesting that pools may persist as a result of enhanced peat decomposition and carbon loss due to oxygenation and or upward supply of alternative electron acceptors from the mineral soil along narrow permeable inorganic esker crests variations in pool depths and radiocarbon dating of peat samples from the pool bottom support a model whereby pools originate at a focus centered along the two esker crests and subsequently spread laterally outwards

the sedimentary architecture of outburst flood eskers a comparison of ground penetrating radar data from bering glacier alaska and skeiðararjokull iceland we present ground penetrating radar gpr profiles that reveal the sedimentary architecture of an esker deposited during a surge associated outburst flood at the bering glacier alaska the wide up flow end of the esker contains a transition from large backset beds to large foreset beds interpreted to reflect composite macroform development in an enlarged part of the conduit by contrast the narrow down flow portion of the esker is dominated by plane beds interpreted to have been deposited where the conduit was constricted and the flow was faster a previously studied outburst esker at skeidararjokull iceland has a similar morphology and stratigraphic architecture this suggests that outburst floods generate distinct depositional signatures in eskers both in terms of morphology and sedimentary architecture identification of these distinct signatures in ancient eskers will help assess the paleohydraulic conditions under which ancient eskers formed and by extension the nature of meltwater drainage systems beneath the laurentide and eurasian ice sheets

landscape formation at the deuteronilus contact in southern isidis planitia mars implications for an isidis sea abstract two of the most widely studied landforms that are associated with a putative ocean that filled the northern hemisphere of mars are 1 the vastitas borealis formation vbf plain units that cover a larger portion of the northern lowlands of mars and 2 a candidate paleoshoreline e g the deuteronilus contact which represents the outer margin of the vbf the vbf and the deuteronilus contact are interpreted to result from a short lived late hesperian ocean that readily froze and sublimated similar landforms are also present in the impact basin of isidis planitia and suggest formation processes comparable to those that formed the vbf and the deuteronilus contact in the northern lowlands our study of the deuteronilus contact in isidis revealed geologic evidence that possibly supports the existence of a late hesperian early amazonian isidis sea for example numerous valleys that are incised into the plains of the southern isidis basin rim between 82 90 e and 3 6 n and trend a few tens of kilometers to the north following the general topographic gradient toward the center of isidis planitia a few of them reach the deuteronilus contact and continue as sinuous ridges in the isidis interior plains iip based on our findings we conclude that the geologic setting along the deuteronilus contact including the valleys and ridges is a result of 1 late hesperian short term fluvial activity 2 a late hesperian early amazonian short lived isidis sea that readily froze 3 subglacial drainage and esker formation and 4 subsequent sublimation of the proposed isidis ice sheet although the fluvio glacial model we introduce in our manuscript cannot fully explain the geologic setting possible alternative formation models including relief inversion and fluvio volcanic scenarios are even less capable in explaining the observed geologic setting along the deuteronilus contact

how sediment promotes narrow rifting application to the gulf of california 1 if the gravitational stress changes related to crustal thinning are large enough to affect the mode of extension then sedimentation should also affect that mode we propose that the weight of sediments reduces the difference in crustal buoyancy forces caused by local crustal thinning allowing a rift to extend more easily in a narrow rift mode we examine the effect of deposition of large amounts of nonlocally derived sediment on extensional style using two dimensional regional scale numerical experiments of extending thick continental crust with varied initial thermal conditions geometries rheological parameters and sedimentation properties depending on initial model conditions the onset of rifting in thick continental crust occurs in the narrow rifting wide rifting or core complex mode with continued extension all cases eventually transition to a narrow rifting mode for a system in wide rift mode moderate to fast sedimentation shortens the time needed to transition to a narrow rift in the gulf of california changes in extensional style correlate with sediment thickness with an earlier transition to narrow rifting in the north versus the south we compare our model results to the extensional history of the gulf of california where sediments may have caused the northern and north central domain of the gulf delfin tiburon and guaymas segments to transition to narrow rifting before the south central domains alarcon segment

eskers in a complete wet based glacial system in the phlegra montes region mars although glacial landsystems produced under warm wet based conditions are very common on earth even here observations of subglacial landforms such as eskers emerging from extant glaciers are rare this paper describes a system of sinuous ridges emerging from the in situ but now degraded piedmont terminus of a late amazonian aged 150 ma glacier like form in the southern phlegra montes region of mars we believe this to be the first identification of martian eskers that can be directly linked to their parent glacier together with their contextual landform assemblage the eskers are indicative of significant glacial meltwater production and subglacial routing however although the eskers are evidence of a wet based regime the confinement of the glacial system to a well defined regionally significant graben and the absence of eskers elsewhere in the region is interpreted as evidence of sub glacial melting as a response to locally enhanced geothermal heat flux rather than climate induced warming these observations offer important new insights to the forcing of glacial dynamic and melting behaviour on mars by factors other than climate

time transgressive deposits of repeated depositional sequences within interlobate glaciofluvial esker sediments in koylio sw finland abstract evidence of conspicuous repeated seasonal to annual deposition of glaciofluvial and glaciolacustrine sequences within a structurally complex interlobate esker segment in sw finland is presented the time transgressive overlapping depositional sequences consist of deposits from two successive melt seasons including three vertically stacked lithofacies associations 1 massive to stratified coarse gravels summer deposits 2 trough and ripple cross stratified fine grained deposits autumn to winter deposits and 3 sandy stratified beds spring deposits the depositional environment of each lithofacies association involves a transition from subglacial or submarginal tunnel to a subaqueous re entrant environment which then passes to a proglacial glaciolacustrine environment the study also presents evidence of headward extension of subglacial tunnel deposits related to the rapid shifting of a tunnel expansion point during the increasing spring discharge which occupied the old tunnel exit this mode of annual deposition has not been reported previously in esker studies the good preservation of the rhythmic lithofacies associations is suggested as resulting from interlobate depositional conditions associated with rapidly decaying icestreams therefore the depositional model may provide a key to recognizing time transgressive interlobate eskers that form an important geomorphological and sedimentological record of meltwater activity during the last deglaciation of the fennoscandian and laurentide ice sheets the identification of time transgressive interlobate eskers and associated palaeo icestream behaviour is an essential step forward for more accurate models of ice sheet behaviour and palaeoclimatic reconstructions

glacial geomorphology of the central barents sea implications for the dynamic deglaciation of the barents sea ice sheet abstract contemporary climate change has resulted in great uncertainty in how glaciers and ice sheets around the earth might evolve it has long been appreciated that the contemporary west antarctic ice sheet wais shares many similarities with the former barents sea ice sheet bsis therefore an increasing number of studies have sought to investigate the barents sea glacial record to better understand marine based glaciation this paper reports the analysis of a new high resolution bathymetric survey covering 55 000 km2 in the central barents sea the relative chronologies of newly mapped glacial landforms such as mega scale glacial lineations grounding zone wedges moraines and crevasse squeeze ridges are used to reconstruct the ice sheet dynamics in the central barents sea our results show that the ice sheet responded dynamically with different periods of retreat advance and stagnation observed these new landform records have been integrated with other geomorphological records in order to reconstruct the retreat pattern of the bsis between 17 14 ka when the fennoscandian ice sheet is thought to have uncoupled from the bsis our data shows that the dynamic drawdown of the ice sheet saddle by ice streams was probably the primary mechanism in separating the two ice sheets after the ice sheets uncoupled the bsis is shown to have retreated episodically with several periods of relative stability geomorphological records such as those from the bsis can be used to constrain ice sheet modelling and will help to develop a clearer understanding of marine based glaciation and the role of ice streams in driving ice sheet evolution

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

mechanisms of englacial conduit formation and their implications for subglacial recharge abstract ideas about the character and evolution of englacial drainage systems have been deeply influenced by the theoretical model developed by shreve 1972 movement of water in glaciers journal of glaciology 11 62 205 214 the shreve model is based on three main assumptions 1 englacial drainage is in steady state 2 englacial water will flow along the steepest hydraulic gradient within the glacier and 3 pressure head equals the pressure of the surrounding ice minus a small component due to melting of the walls the shreve model has been widely adopted as a fundamental component of englacial drainage theory there is no evidence however that the model provides a realistic picture of actual glacial drainage systems to evaluate shreve s theory we used speleological techniques to directly survey englacial conduits we mapped a total of 8 25 km of passage in 27 distinct englacial conduits in temperate polythermal cold based and debris covered glaciers between 2005 and 2008 new information reported here is supplemented by published data on 40 other englacial conduits located worldwide and surveyed to ice depths of 176 m using speleological techniques in all cases englacial drainage systems consisted of a single unbranching conduit englacial conduit morphologies were found to be intimately linked to the orientation of a glacier s principal stresses or the presence of pre existing lines of high hydraulic conductivity if a sufficient supply of water is available hydrofracturing forms vertical conduits in zones of longitudinal extension and subhorizontal conduits where longitudinal stresses are compressive on unfractured glacier surfaces relatively shallow subhorizontal conduits with migrating nickpoints form by cut and closure provided channel incision is significantly faster than surface lowering conduits can also form along permeable debris filled crevasse traces that connect supraglacial lake basins of different potential our results suggest that shreve type englacial drainage systems do not exist and implies that englacial conduits can only penetrate through thick ice to recharge the bed where supraglacial water bodies either intersect or are advected through zones of acceleration

recent basal melting of a mid latitude glacier on mars evidence for past basal melting of young late amazonian debris covered glaciers in mars mid latitudes is extremely rare thus it is widely thought that these viscous flow features vffs have been perennially frozen to their beds we identify an instance of recent localized wet based mid latitude glaciation evidenced by a candidate esker emerging from a vff in a tectonic rift in tempe terra eskers are sedimentary ridges deposited in ice walled meltwater conduits and are indicative of glacial melting we compare the candidate esker to terrestrial analogues present a geomorphic map of landforms in the rift and develop a landsystem model to explain their formation we propose that the candidate esker formed during a transient phase of wet based glaciation we then consider the similarity between the geologic setting of the new candidate esker and that of the only other candidate esker to be identified in association with an existing mid latitude vff both are within tectonic graben rifts proximal to volcanic provinces finally we calculate potential basal temperatures for a range of vff thicknesses driving stresses mean annual surface temperatures and geothermal heat fluxes which unlike previous studies include the possible role of internal strain heating strain heating can form an important additional heat source especially in flow convergence zones or where ice is warmer due to elevated surface temperatures or geothermal heat flux elevated geothermal heat flux within rifts perhaps combined with locally elevated strain heating may have permitted wet based glaciation during the late amazonian when cold climates precluded more extensive wet based glaciation on mars

geophysical characterization of late quaternary glaciofluvial complex and glacial stratigraphy in the satakunta sandstone area koylio southwest finland

subglacial hydrology in north western germany during the last glaciation groundwater flow tunnel valleys and hydrological cycles abstract numerical modelling of groundwater dynamics in an overpressured system of subglacial aquifers and aquitards under the marginal portion of the scandinavian ice sheet in northwestern germany has been coupled with calculations of basal meltwater production rates and with field evidence of meltwater erosional features largely fine grained subglacial sediments with relatively low hydraulic conductivities had a capacity to drain only about 25 of all basal meltwater produced in the relevant subglacial catchment area the rest of the meltwater was evacuated through tunnel valleys in spontaneous outburst events subglacial drainage cycles are proposed in which each cycle begins with meltwater drainage through the substratum groundwater flow followed by water ponding at the ice bed interface and ends in catastrophic meltwater releases through tunnel valleys

morphometry of bedrock meltwater channels on antarctic inner continental shelves implications for channel development and subglacial hydrology abstract expanding multibeam bathymetric data coverage over the last two decades has revealed extensive networks of submarine channels incised into bedrock on the antarctic inner continental shelf the large dimensions and prevalence of the channels implies the presence of an active subglacial hydrological system beneath the past antarctic ice sheet which we can use to learn more about inaccessible subglacial processes here we map and analyse over 2700 bedrock channels situated across 100 000 km2 of continental shelf in the western antarctic peninsula and amundsen sea to produce the first inventory of submarine channels on the antarctic inner continental shelf morphometric analysis reveals highly similar distributions of channel widths depths cross sectional areas and geometric properties with subtle differences between channels in the western antarctic peninsula compared to those in the amundsen sea at 75 3400 m wide 3 280 m deep 160 290 000 m2 in cross sectional area and typically 8 times as wide as they are deep the channels have similar morphologies to tunnel valleys and meltwater channel systems observed from other formerly glaciated landscapes despite differences in substrate geology and glaciological regime we propose that the antarctic bedrock channels formed over multiple glacial cycles through the episodic drainage of at least 59 former subglacial lakes identified on the inner continental shelf

the harricana glaciofluvial complex abitibi region quebec its genesis and implications for meltwater regime and ice sheet dynamics abstract interlobate moraines have been defined by their relationshio to adjacent landforms and sediments with minimal reference to any genesis suggested from their own geomorphology and sedimentology a case in point is the harricana interlobate moraine the harricana complex a relatively continuous linear accumulation of glaciofluvial sediments is investigated in terms of its geomorphology sedimentology stratigraphic context and landform associations for the portion between latitudes 48 n and 50 n the complex is narrower to the north than to the south in the narrower northern part better rounding and poorer preservation of less resistant clasts suggest more vigorous transport in a narrower conduit the inverse in the wider southern part favours less vigorous flows and higher deposition rates these inferences together with unidirectional paleoflows towards the ice margin and the relatively continuous upslope path of the southward widening complex favour synchronous formation of the harricana complex in a continuous closed conduit beneath an ice sheet which thinned southward subaqueous fans and grounding line deposits with fine gravel and sandy in phase wave structures in the south may have been deposited in subglacial cavities adjacent to the complex or later deposited in reentrants in calving ice fronts the basic building blocks of the harricana complex are gravel facies which indicate generally high energy but unsteady transport these facies are arranged into macroforms composite and oblique accretion avalanche bed oaab macroforms are attributed to deposition by unsteady and non uniform flows in conduit enlargements pseudoanticlinal macroforms were deposited in relatively narrow conduit segments of uniform width gravel sand couplets register flow unsteadiness perhaps related to variations in supraglacial metlwater supply the origin of the harricana complex as a mainly synchronous subglacial landform is linked to formation of adjacent streamlined bedforms and bedrock erosional marks by meltwater outburst floods the complex is located where the orientation of these subglacial bedforms indicate strong flow convergence post flood ice sheet collapse along this convergence zone initiated redirection of ice flow resulting in cross cutting striae later subglacial meltwater systems followed new hydraulic gradients toward this trough of thinner ice forming a major conduit and depositing the harricana glaciofluvial complex

high energy sedimentation creag aoil spean bridge scotland implications for meltwater movement and storage during loch lomond stadial younger dryas ice retreat this paper examines the origin and significance of loch lomond stadial younger dryas gravel deposits at creag aoil spean bridge scotland sedimentation into ice dammed lakes in glen roy and glen spean associated with shorelines at 260 m 325 m and 350 m is well documented yet little is known about later lower level lakes near spean bridge excavations on the northern flanks of the lundy channel revealed exposures into a 35 40 m thickness of sand and gravel these sediments reflect deposition in a subaqueous environment experiencing repeated short lived periods of high energy subaerial deposition deformation structures within subaqueous deposits are associated with at least two ice push events this study presents new evidence for the existence of ice dammed lakes at elevations between 260 m and 113 m and for periodic jokulhlaups draining southwest via the lundy channel active glacier ice associated with the deposits flowed northwest to southeast driving meltwater across the great glen to the lundy channel glacier retreat was punctuated by periodic minor readvances progressive ice retreat was accompanied by ice thinning and changes in ice flow direction and subglacial meltwater routing these findings add to knowledge of loch lomond stadial deglaciation around spean bridge and have implications for our understanding of lacustrine glacier margins during deglaciation copyright 2003 john wiley sons ltd keywords ice dammed lake subaqueous outwash jokulhlaups ice push structures scotland

subglacial jokulhlaup deposition jotunheimen norway abstract the aim of this paper is to discuss the origin of a linear boulder deposit near the mjolkedalsbreen jotunheimen norway subglacial fluvial deposition is suggested by palaeoflow indicators showing flow directions uphill along the axis of a ridge like deposit and the close association of this deposit with an ice contact boulder delta peak discharges of repeated jokulhlaups from the former ice dammed ovre mjolkedalsvatn were estimated at 1188 m3 s 1 using evidence derived from the proglacial jokulhlaup routeway former ice tunnel dimensions and flow conditions associated with the ridge like deposit were derived from a simple pipe flow equation flow velocities of 9 8 11 6 m s 1 and shear stresses of 1440 2018 n m2 were reconstructed for a tunnel less than 3 m in average height and 45 m wide such flows would have been capable of transporting boulders of greater than 3 m in diameter as traction load and material of gravel cobble size in suspension material of this size has been deposited downflow as an ice contact delta linear ridges of boulder gravel with up slope gradients found in association with ice contact deposits in other formerly glaciated areas may similarly be of jokulhlaup origin

genesis of an esker like ridge over the southern fraser plateau british columbia implications for paleo ice sheet reconstruction based on geomorphic inversion abstract robust interpretations of meltwater systems operating during ice sheet decay are integral to reconstructing deglacial patterns and style yet over reliance on meltwater landform morphology with limited attention to morpho sedimentary relationships and basin scale geomorphic and stratigraphic context can lead to unreliable geomorphic inversion based paleo ice sheet reconstructions this problem is illustrated by the evolution of young lake esker like ridge yler formed in the young lake basin ylb on bc s southern fraser plateau during decay of the last cordilleran ice sheet cis we integrate data from digital elevation models aerial photographs sedimentary outcrops water wells and shallow geophysics ground penetrating radar electrical resistivity tomography previous interpretations of yler as both an esker and an ice contact poorly sorted stratified deposit emplaced by westerly flowing meltwater imply an eastward retreating ice margin geophysical data from a flat topped component of yler reveal slipface and planar bedded sand and gravel overlying lacustrine sediments characteristic of a hjulstrom delta eastward dipping foresets in a gilbert delta exist at the eastern terminus contextually our observations suggest despite esker like morphology yler was not deposited within a subglacial ice tunnel instead it formed through deposition of subaerial outwash between and or on dead ice in front of a regionally backwasting ice margin the complex deglacial evolution of ylb including a drainage reversal and formation of two glacial lakes supports northwestward backwasting of the cis and dead ice within ylb we conclude that accurate geomorphic inversion of meltwater landforms for deglacial paleo ice sheet reconstruction requires knowledge of landform scale morpho sedimentary relationships and basin scale geomorphic and stratigraphic context

landform assemblage in isidis planitia mars evidence for a 3 ga old polythermal ice sheet abstract the floor of isidis planitia a giant impact basin located close to the martian equator exhibits a landform assemblage nicknamed thumbprint terrain made of arcuate ridges aligned cones isolated cones cone fields associated with a peripheral network of sinuous ridges linear depressions and mounds from a new comprehensive mapping initiative of these landforms and from comparisons with terrestrial analogues ribbed moraines dirt cones kettle holes eskers tunnel valleys and moraine plateaux we demonstrate that this distinctive assemblage is a glacial landsystem inherited from the presence of a massive polythermal ice sheet over the basin during the hesperian the flow of the ice sheet was controlled by its basal thermal regime wet based conditions led to the formation of arcuate ridges and aligned cones in most parts of the basin while a negative geothermal anomaly due to impact related crustal thinning was responsible for cold based conditions in its central part where only isolated cones and cones fields are present sinuous ridges linear depressions and mounds at the basin margins are interpreted as relicts of a radial network of subglacial channels which drained the glacial meltwater produced within the interior of the ice sheet across its cold based periphery

the high resolution imaging science experiment hirise during mro s primary science phase psp the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro acquired 8 terapixels of data in 9137 images of mars between october 2006 and december 2008 covering 0 55 of the surface images are typically 5 6 km wide with 3 color coverage over the central 20 of the swath and their scales usually range from 25 to 60 cm pixel nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models dtms completed these data have led to some of the most significant science results new methods to measure and correct distortions due to pointing jitter facilitate topographic and change detection studies at sub meter scales recent results address noachian bedrock stratigraphy fluvially deposited fans in craters and in or near valles marineris groundwater flow in fractures and porous media quasi periodic layering in polar and non polar deposits tectonic history of west candor chasma geometry of clay rich deposits near and within mawrth vallis dynamics of flood lavas in the cerberus palus region evidence for pyroclastic deposits columnar jointing in lava flows recent collapse pits evidence for water in well preserved impact craters newly discovered large rayed craters and glacial and periglacial processes of particular interest are ongoing processes such as those driven by the wind impact cratering avalanches of dust and or frost relatively bright deposits on steep gullied slopes and the dynamic seasonal processes over polar regions hirise has acquired hundreds of large images of past present and potential future landing sites and has contributed to scientific and engineering studies of those sites warming the focal plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions

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

volcanism induced local wet based glacial conditions recorded in the late amazonian arsia mons tropical mountain glacier deposits abstract the tropical mountain glacial fan shaped deposit fsd to the northwest of the arsia mons volcano on mars contains numerous glacial and volcanic landforms while most of the glacial landforms are interpreted to have formed by cold based glacial processes several glacial landforms near glaciovolcanic edifices are more consistent with localized wet based glacial processes these landforms include ribbed moraines which suggest local thermal transitions between wet and cold based ice thrust block moraines whose formation is typically assisted by the presence of subglacial water streamlined knobs that we interpret to have been sculpted by ice sliding along its base and a braided outflow channel the presence and association of these features together with evidence of both subglacial volcanic eruptions and local ice marginal advances favor polythermal glaciers with localized wet based conditions we propose that lava to ice heat transfer during the eruption of the glaciovolcanic edifices caused the arsia mons paleoglacier to melt at its base in some areas resulting in these locally wet based glacial conditions a polythermal glacier provides more potential microbial habitats and more connectivity between habitats than does a cold based glacier and we review glacial and glaciovolcanic habitats on earth that may provide insight into the likelihood of potential microbial habitats within the arsia mons fsd on mars

controls on the location morphology and evolution of complex esker systems at decadal timescales breiðamerkurjokull southeast iceland this paper uses detailed mapping of eskers to address three questions which are important for reconstructing meltwater behaviour beneath contemporary and ancient ice masses what controls the morphology of simple and complex esker systems how do esker systems evolve through time and are esker patterns compatible with the groundwater controlled hydraulic spacing of esker tunnels esker crestlines and widths are mapped on the brei amerkurjokull foreland for eight time slices between 1945 and 2007 from high resolution 50 cm aerial photography permitting their long term morphological evolution to be analysed in a high level of detail we find that complex eskers develop where meltwater and sediment is abundant such that sediment clogs channels forming distributary eskers isolated eskers are simpler and smaller and reflect less abundant meltwater and sediment which is unable to clog channels eskers may take several decades to emerge from outwash deposits containing buried ice and can increase or decrease in size when ice surrounding and underlying them melts out it has been suggested that groundwater channel coupling dictates the spacing between eskers at brei amerkurjokull our results do not dispute this but suggest that the routing of sediment and meltwater through medial moraines is an additional important control on esker location and spacing these results may be used to better understand the processes surrounding esker formation in a variety of geographical settings enabling a more detailed understanding of the operation of meltwater drainage systems in sub marginal zones beneath glaciers and ice sheets this article is protected by copyright all rights reserved

subglacial basins their origin and importance in glacial systems and landscapes closed topographic basins are found beneath contemporary ice masses and within the footprint of former ice masses in all glaciated regions we present the first integrated review of subglacial basin occurrence and formation and the implications of such basins for glaciological processes and the evolution of landscape our purpose is to motivate research in areas where understanding of basin origin and process significance is weak basins on the order of 10 102 m deep and 102 103 m long are produced by glacial erosion of subglacial rock and or sediment and are known as overdeepenings outlet and valley glaciers can overdeepen their beds far below sea level or local fluviatile base level larger basins typically in ice sheet contexts may have a pre glacial usually tectonic origin subglacial basins are important glaciologically because they require ice water and sediment to ascend an adverse subglacial slope in order to exit the glacial system the efficiency of which is dependent upon the gradient of the adverse slope and that of the ice surface basins thus influence subglacial drainage system morphology and transmissivity the thickness and distribution of basal ice and sediment layers and the mechanisms and dynamics of ice flow adverse gradients that exceed 11 times that of the ice surface may even permit the formation of subglacial lakes we speculate that in comparison to ice masses with few or no subglacial basins those with numerous or very large basins may respond to climatic changes with unexpected vigour in addition erosion rates and transport pathways of water and sediment through the glacial system and the expression of these processes in the sediment and landform record may be unexpectedly complex further our review shows that in a warming climate ice masses resting on adverse slopes will be vulnerable to rapid and potentially catastrophic retreat new lakes in subglacial basins exposed by mountain glacier retreat will present an increasing hazard and subglacial lakes may drain catastrophically on even longer time scales we speculate that the glacial excavation and post glacial filling of basins in mountainous regions should contribute importantly to climate related changes in isostasy and relief although the controls on overdeepening and their influence on other glacial and landscape processes remain uncertain we hypothesise that overdeepened glacial systems reflect an equilibrium ice bed geometry that maximises the efficiency of ice discharge improved understanding of overdeepening processes especially overdeepened bed hydrology is therefore necessary to understand fully the dynamic behaviour of valley and outlet glaciers and thus the fate of earth s largest ice masses

fresh shallow valleys in the martian midlatitudes as features formed by meltwater flow beneath ice significant numbers of valleys have been identified in the martian midlatitudes 30 60 n s spatially associated with extant or recent ice accumulations many of these valleys date to the amazonian but their formation during these cold dry epochs is problematic in this study we look in detail at the form distribution and quantitative geomorphology of two suites of these valleys and their associated landforms in order to better constrain the processes of their formation since the valleys themselves are so young and thus well preserved uniquely we can constrain valley widths and courses and link these to the topography from the mars orbiter laser altimeter and high resolution stereo camera data we show that the valleys are both qualitatively and quantitatively very similar despite their being 5000 km apart in different hemispheres and around 7 km apart in elevation buffered crater counting indicates that the ages of these networks are statistically identical probably forming during the late amazonian 100 ma in both localities at least tens of valleys cross local drainage divides apparently flowing uphill we interpret these uphill reaches to be characteristic of flow occurring beneath a now absent relatively thin order 101 102 m regionally extensive ice cover ridges and mounds occasionally found at the foot of these valley systems are analogous to eskers and aufeis like refreezing features on the basis of their interaction with these aufeis like mounds we suggest that this suite of landforms may have formed in a single short episode perhaps order of days probably forced by global climate change

ice fracturing during jokulhlaups implications for englacial floodwater routing and outlet development theoretical studies of glacial outburst floods jokulhlaups assume that i intraglacial floodwater is transported efficiently in isolated conduits ii intraglacial conduit enlargement operates proportionally to increasing discharge iii floodwater exits glaciers through pre existing ice marginal outlets and iv the morphology and positioning of outlets remains fixed during flooding direct field observations together with historical jokulhlaup accounts confirm that these theoretical assumptions are not always correct this paper presents new evidence for spatial and temporal changes in intraglacial floodwater routing during jokulhlaups secondly it identifies and explains the mechanisms controlling the position and morphology of supraglacial jokulhlaup outlets and finally it presents a conceptual model of the controls on supraglacial outbursts field observations are presented from two icelandic glaciers skei ararjokull and solheimajokull video footage and aerial photographs taken before during and after the skei ararjokull jokulhlaup and immediately after the solheimajokull jokulhlaup reveal changes in floodwater routing and the positioning and morphology of outlets field observations confirm that glaciers cannot transmit floodwater as efficiently as previously assumed rapid increases in jokulhlaup discharge generate basal hydraulic pressures in excess of ice overburden under these circumstances floodwater can be forced through the surface of glaciers leading to the development of a range of supraglacial outlets the rate of increase in hydraulic pressure strongly influences the type of supraglacial outlet that can develop steady increases in basal hydraulic pressure can retro feed pre existing englacial drainage whereas transient increases in pressure can generate hydraulic fracturing the position and morphology of supraglacial outlets provide important controls on the spatial and temporal impact of flooding the development of supraglacial jokulhlaup outlets provides a new mechanism for rapid englacial debris entrainment

rothlisberger channel theory its origins and consequences the theory of channelized water flow through glaciers most commonly associated with the names of hans rothlisberger and ron shreve and their 1972 papers in the journal of glaciology was developed at a time when interest in glacier bed processes was expanding and the possible relationship between glacier sliding and water at the bed was becoming of keen interest the r channel theory provided for the first time a physically based conceptual model of water flow through glaciers the theory also marks the emergence of glacier hydrology as a glaciological discipline with goals and methods distinct from those of surface water hydrology

thermal conditions at the bed of the laurentide ice sheet in maine during deglaciation implications for esker formation the university of maine ice sheet model was used to study basal conditions during retreat of the laurentide ice sheet in maine within 150 km of the margin basal melt rates average 5m m a 1 during retreat they decline over the next 100 km so areas of frozen bed develop in northern maine during retreat by integrating the melt rate over the drainage area typically subtended by an esker we obtained a discharge at the margin of 1 2 m 3 s 1 while such a discharge could have moved the material in the katahdin esker it was likely too low to build the esker in the time available additional water from the glacier surface was required temperature gradients in the basal ice increase rapidly with distance from the margin by conducting upward into the ice all of the additional viscous heat produced by any perturbation that increases the depth of flow in a flat conduit in a distributed drainage system these gradients inhibit the formation of sharply arched conduits in which an esker can form this may explain why eskers commonly seem to form near the margin and are typically segmented with later segments overlapping onto earlier ones

icelandic jokulhlaup impacts implications for ice sheet hydrology sediment transfer and geomorphology abstract glaciers and ice sheets erode entrain and deposit massive quantities of debris fluxes of subglacial meltwater exert a fundamental control on ice dynamics and sediment transport budgets within many glacial systems outburst floods jokulhlaups constitute high magnitude high frequency fluxes of meltwater relative to normal ablation controlled discharge this paper presents a synthesis of research on recent icelandic jokulhlaups and their geomorphological and sedimentary impact we identify jokulhlaup impacts within subglacial englacial and proglacial settings and discuss their wider significance for ice sheet hydrology sediment transfer and geomorphology because jokulhlaups erode deposit and re work sediment simultaneously they usually cause significant glaciological and sedimentological impacts jokulhlaups that propagate as subglacial flood waves often produce widespread hydromechanical disruption at the glacier base recent icelandic jokulhlaups have been recognised as highly efficient agents of reworking subglacial sediment and glacial sediment entrainment models of jokulhlaup impact therefore need to encompass the sub and englacial environment in addition to the proglacial zone where research has traditionally been focussed most jokulhlaups transport sediment to proglacial sandar and often directly to oceans where preservation potential of the impact is greater proglacial jokulhlaup deposits form distinctive sedimentary assemblages coupled with suites of high energy erosional landforms this study of modern jokulhlaup processes and sedimentary products may be useful for the interpretation of meltwater processes associated with quaternary ice sheets

triangular shaped landforms reveal subglacial drainage routes in sw finland abstract the aim of this study is to present the first evidence of triangular shaped till landforms and related erosional features indicative of subglacial drainage within the ice stream bed of the scandinavian ice sheet in finland previously unidentified grouped patterns of quaternary deposits with triangular landforms can be recognized from lidar based dems the triangular landforms occur as segments within geomorphologically distinguishable routes that are associated with eskers the morphological and sedimentological characteristics as well as the distribution of the triangular landforms are interpreted to involve the creep of saturated deforming till flow and pressure fluctuations of subglacial meltwater associated with meltwater erosion there are no existing models for the formation of this kind of large scale drainage systems but we claim that they represent an efficient drainage system for subglacial meltwater transfer under high pressure conditions our hypothesis is that the routed large scale subglacial drainage systems described herein form a continuum between channelized eskers and more widely spread small scale distributed subglacial drainage moreover the transition from the conduit dominated drainage to triangular shaped subglacial landforms takes place about 50 60 km from the ice margin we provide an important contribution towards a more realistic representation of ice sheet hydrological drainage systems that could be used to improve paleoglaciological models and to simulate likely responses of ice sheets to increased meltwater production

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

an ice sheet scale comparison of eskers with modelled subglacial drainage routes eskers record the signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage in this paper we compare the spatial pattern of eskers beneath the former laurentide ice sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice sheet model perhaps surprisingly we show that eskers predominantly occur in regions where modelled subglacial water flow is low eskers and modelled subglacial drainage routes were found to typically match over distances of 10 km and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation this supports a time transgressive esker pattern with formation in short 10 km segments of conduit close behind a retreating ice margin and probably associated with thin stagnant or sluggish ice esker forming conduits were probably dominated by supraglacially fed meltwater inputs we also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo ice stream locations the paucity of eskers along the terrestrial portion of these palaeo ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast flowing ice

evidence for remnants of ancient ice rich deposits mangala valles outflow channel mars high resolution spacecraft data reveal the presence of a distinctive unit on the upper reaches of the floor of mangala valles an ancient outflow channel on mars in contrast to abundant evidence for scour intense erosion and hydrodynamic shaping typical of the floors and margins of mangala and other outflow channels this unit is smooth surfaced has cuspate margins is superposed on the scoured valley floor and is extensively pitted we interpret this unit to be the sublimation lag deposit derived from an ice thermal boundary layer on the aqueous flood that formed the outflow channel system and the remnant of floodwaters trapped in channel lows this interpretation further supports the likelihood that climate conditions at the time of emplacement were similar to the hyper arid cold desert conditions of today frozen floodwaters from the ancient martian subsurface could still be preserved in these deposits representing attractive and accessible exobiological exploration objectives

towards a morphogenetic classification of eskers implications for modelling ice sheet hydrology abstract validations of paleo ice sheet hydrological models have used esker spacing as a proxy for ice tunnel density changes in crest type cross sectional shape along esker ridges have typically been attributed to the effect of changing subglacial topography on hydro and ice dynamics and hence subglacial ice tunnel shape these claims assume that all eskers formed in subglacial ice tunnels and that all major subglacial ice tunnels produced a remnant esker we identify differences in geomorphic context sinuosity cross sectional shape and sedimentary architecture by analysing eskers formed at or near the margins of the last cordilleran ice sheet on british columbia s southern fraser plateau and propose a morphogenetic esker classification three morphogenetic types and 2 subtypes of eskers are classified based on differences in geomorphic context ridge length sinuosity cross sectional shape and sedimentary architecture using geophysical techniques and sedimentary exposures they largely record seasonal meltwater flows and glacial lake outburst floods glofs through sub en and supraglacial meltwater channels and ice walled canyons general principles extracted from these interpretations are 1 esker ridge crest type and sinuosity strongly reflect meltwater channel type eskers formed in subglacial conduits are likely to be round crested with low sinuosity except where controlled by ice structure or modified by surging and contain faults associated with flank collapse eskers formed near or at the ice surface are more likely to be sharp crested highly sinuous and contain numerous faults both under ridge crest lines and in areas of flank collapse 2 esker ridges containing numerous flat crested reaches formed directly on the land surface in ice walled canyons unroofed ice tunnels or in ice tunnels at atmospheric pressure and therefore likely record thin or dead ice 3 eskers containing macroforms exhibiting headward and downflow growth likely record flood scale flows possibly glofs where a lake can be inferred these conclusions suggest that esker crest type sinuosity and geomorphic context when understood along with sedimentary architecture largely reflect formational position with respect to the ice surface reconstructions of ice sheet hydrology need to account for variation in esker morphology because basing hydrodynamic inferences on the presence or absence of an esker alone ignores encoded differences in water source supply flow magnitude and frequency and conduit position

late wisconsin ice surface profile calculated from esker paths and types katahdin esker system maine abstract values of the gradient of the former ice surface can be inferred at points along a flow line from deviations of esker paths or transitions in esker type and numerically integrated to give the profile a profile calculated in this way shows that during formation of the katahdin esker system about 12 700 yr ago the ice thickness at distances of 10 20 50 100 and 140 km from the terminus which is about two thirds of the distance to the ice divide was approximately 200 300 600 750 and 900 m the terminal reach was computed by assuming an unknown uniform basal drag and matching the profile to its known elevation at the terminus and known gradient 10 km upglacier correction for isostatic rebound based on the elevations of contemporaneous deltas and of the marine limit proved unnecessary because the tilt due to the difference in uplift at the two ends of the profile is only 0 1 m km 1 with other plausible assumptions as to sea levels in the past elevations of the marine limit or exact location of the terminus the profile could be as much as roughly 100 m higher it hits mount katahdin about 500 m below its summit which is at 1600 m in agreement with the geological evidence farther west the steepening of the upper part of the profile suggests that the mountain dammed and diverted the ice basal drag computed from the profile varies from about 20 kpa 0 2 bar near the terminus to 30 kpa 0 3 bar at 100 km to 70 kpa 0 7 bar at 140 km the relatively low values away from the influence of mount katahdin agree with independent evidence from deep sea cores of substantial late wisconsin ice sheet thinning without comparable areal reduction the method has potential for application over wide areas that were occupied by the laurentide and scandinavian ice sheets

the banded terrain on northwestern hellas planitia new observations and insights into its possible formation abstract northwestern hellas planitia hosts landforms that are unique on mars e g the so called honeycomb and banded aka taffy pull terrains recently robust formation models for the 6 km large honeycomb depressions involving salt or ice diapirism have been formulated however the nature of the banded terrain a 30 000 km area characterized by a decameter to kilometer scale pattern of curvilinear troughs has remained elusive while previous interpretations range from deep seated honeycomb related outcrops to a younger veneer recent reports of putative periglacial features e g potential thermokarst strongly indicate it to be a relatively thin volatile related surface unit in order to further constrain the origin and nature of the banded terrain we investigated the northwestern hellas basin floor employing various datasets we mapped the banded terrain s extent at high precision showing that it partially superposes the honeycomb terrain but also occurs up to 240 km away from it via stratigraphic analyses and crater size frequency measurements we bracketed the age of the banded terrain between 1 9 and 3 7 ga furthermore the banded terrain can be differentiated into two types ridged and creviced with the former predominantly occurring among the lowest reaches of the terrain s 2 km topographic extent we also produced a grid map 2 2 km box size of the entire banded terrain and identified no large scale 25 km band pattern and no correlation between local slope and band orientation because of this we submit that regional tectonics or gravity driven flow down modern topography are unlikely to have played decisive roles for banded terrain formation instead we observed numerous locations where band slabs appear to have broken off and subsequently rotated as well as cusps that seem to have resulted from buckling based on this we suggest that the banded terrain experienced both ductile deformation as well as brittle failure on or near the surface despite certain similarities neither salt as salt glaciers lava sheets or land based glaciers are in agreement with the extensive curvilinear texture and topographic geologic setting of the banded terrain ice shelf margins on the other hand can produce surface textures akin to the banded terrain in both form and scale even including cusps and broken off rotated blocks however an ice covered sea between 1 9 and 3 7 ga ago is not indicated by the geologic inventory of the hellas basin which previous investigations found to lack any landforms indicative of a standing body of water instead we identified several sinuous ridges terminating at plains covered by smaller braiding ridges which we interpret as eskers and glacial sandurs respectively as both are embayed and partially covered by the banded terrain we tentatively propose an alternative subglacial model of the banded terrain having formed as wet till that was viscously deformed according to the stress fields created by the ice overburden pressure in conjunction with bed topography although this formation model remains inconclusive it is in agreement with climate models suggesting obliquity excursions and a denser early amazonian atmosphere to have caused ice accumulation in the adjacent northwestern hellas basin rim thus potentially enabling flow onto the floor entailing subglacial banded terrain formation

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

the carstairs kames lanarkshire scotland morphology sedimentology and formation the carstairs kames have been the subject of debate for over 150 yr a synthesis of previous work along with new sedimentological data is used to reappraise this classic british esker locality three morphological elements are recognised i large sinuous and anastomosing ridges ii large irregular linear mounds and iii small low and irregular mounds the main ridge system is composed of a core of boulder gravel with sand pebble gravel above and adjacent to the core the large linear mounds contain a varied facies range which include glaciolacustrine sediments deltaic sequences laminites and dropstones debris flows and glaciofluvial channel systems all the deposits both in the main ridges and in the adjacent linear mounds contain syn and post depositional subsidence structures including normal faults synclinal folds and growth faults a range of potential origins for these landforms is reviewed and it is suggested that glaciofluvial sedimentation in a supraglacial environment controlled by a topography of ice cored ridges is the most appropriate depositional model 1997 john wiley sons ltd

sedimentology of a glaciofluvial landsystem lough ree area central ireland implications for ice margin characteristics during devensian deglaciation eskers in a glaciofluvial landsystem in the lough ree area central ireland exhibit two orientations the most southerly esker in the area the athlone esker forms part of a dendritic esker system with paleocurrent directions indicating eastward drainage while the rooskagh esker and associated eskers and kames immediately to the north were formed during southward drainage sediments indicate that sharp crested steep sided sections of both ridges were formed within subglacial tunnels while fan shaped and flat topped areas were formed as subaqueous outwash fans and deltas in standing water immediately in front of an ice margin the deposition of ice marginal deposits indicating southward paleoflows against the side of the eastward flowing athlone esker indicates a 90 shift in the direction of ice surface slope and a similar shift in the likely orientation of the ice margin the absence of any evidence of intermediate ice or water flow directions indicates that the shift reflects a recession of ice followed by a readvance from the north

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

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

evidence of volcanic and glacial activity in chryse and acidalia planitiae mars abstract chryse and acidalia planitiae show numerous examples of enigmatic landforms previously interpreted to have been influenced by a water ice rich geologic history these landforms include giant polygons bounded by kilometer scale arcuate troughs bright pitted mounds and mesa like features to investigate the significance of the last we have analyzed in detail the region between 60 n 290 e and 10 n 360 e utilizing hirise high resolution imaging science experiment images as well as regional scale data for context the mesas may be analogous to terrestrial tuyas emergent sub ice volcanoes although definitive proof has not been identified we also report on a blocky unit and associated landforms drumlins eskers inverted valleys kettle holes consistent with ice emplaced volcanic or volcano sedimentary flows the spatial association between tuya like mesas ice emplaced flows and further possible evidence of volcanism deflated flow fronts volcanic vents columnar jointing rootless cones and an extensive fluid rich substratum giant polygons bright mounds rampart craters allows for the possibility of glaciovolcanic activity in the region landforms indicative of glacial activity on chryse acidalia suggest a paleoclimatic environment remarkably different from today s climate changes on mars driven by orbital obliquity changes or giant outflow channel activity could have resulted in ice sheet related landforms far from the current polar caps

major episodes of geologic history of isidis planitia on mars abstract we have mapped the area of isidis planitia 1 27 n 75 103 e in order to assess the geologic history of this region using modern data sets such as mola topography and the high resolution images provided by the hrsc ctx and hirise cameras results of our mapping show that the geologic history of isidis planitia consists of three principal episodes 1 impact dominated episode noachian until 3 8 ga during this time the oldest materials in the study area were formed mostly by impact reworking and mass wasting other processes e g volcanism and fluvial glacial activity likely operated at this time but played a subordinate role 2 an episode related to volcanic and fluvial glacial activities late noachian early amazonian 3 8 2 8 ga volcanism appears as the most important process at the beginning of this episode 3 8 3 5 ga and was responsible for the formation of a large circum isidis volcanic province by the early hesperian epoch volcanic materials covered large portions of the isidis rim almost completely buried the previous crater record on the floor of the isidis basin and probably were the major contributors to the filling of the basin fluvial glacial processes prevailed closer to the end of the episode early hesperian early amazonian 3 5 2 8 ga and were responsible for widespread resurfacing in the isidis planitia region mostly at 3 1 3 4 ga glaciers and or ice sheets probably resulted in a massive glaciation of the rim and the floor of the isidis basin the total volume of material eroded from the isidis rim by glacial and fluvial activity is estimated to be about 35 000 50 000 km 3 which is equivalent to a composite layer about 40 60 m thick on entire floor of the basin more important however is that the eroded materials were likely saturated with ice water and could form wet deposits on the floor 3 wind dominated episode since early amazonian 2 8 ga wind activity dominated the later geologic history of isidis planitia but resulted only in minor modification of the surface

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

extensive hesperian aged south polar ice sheet on mars evidence for massive melting and retreat and lateral flow and ponding of meltwater local and regional mars orbiter laser altimeter mola topographic data support the presence of an extensive hesperian aged volatile rich south polar deposit the dorsa argentea formation hd and related units underlying the present amazonian aged polar cap api residual ice and apl layered terrain and covering a surface area that could be as large as 2 94 106 km2 about 2 of the surface of mars over twice the area of the present amazonian aged south polar deposits the deposit characteristics indicate that it contained significant quantities of water ice in amounts comparable to present day polar deposits several lines of evidence for melting indicate that the ice sheet deposits underwent melt back and liquid water drainage into surrounding lows including a large valley near the crater schmidt and the argyre basin narrow sinuous ridges lie in a broad linear depression extending from a high near the present polar cap continuously downslope to near the distal portion of hd the new topographic data support the interpretation of these ridges as eskers representing meltwater distribution networks at the base of the receding deposit extensive development of large pits and depressions cavi have previously been interpreted as eolian etching or basal melting of ice rich deposits analysis of mola topography supports the interpretation that they represent basal melting of ice rich deposits and shows that they have links to the esker systems volumetric considerations and topographic lineations suggest that some of the basal melting occurred beneath regions presently occupied by apl and that some of the liquid water formed ponds and lakes in the distal parts of hd the presence of pedestal craters is further evidence of the removal of extensive volatile rich deposits and contributes to the quantitative measure of the former deposit thickness where did the melt products go inspection of the margins of the dorsa argentea formation reveals several large channels that begin there and drain downslope for distances between 900 and 1600 km onto the floor of the argyre basin some 3 5 4 0 km below their origin these channels do not exhibit tributaries their broad lateral distribution supports other evidence that deposit melting was areally very widespread and volumetrically significant and that a large part of the meltwater entered the surface distribution system and was deposited on the floor of the argyre basin over 1000 km away estimates of the present deposit thicknesses together with amounts of the deposit removed by meltback suggest that the original volume could have been as much as 5 9 106 km3 equivalent to a global layer of water 20 m deep if the deposit consisted of 50 volatiles a portion of these volatiles migrated across the surface to pond in adjacent valleys and basins and into the groundwater system a significant portion of the volatiles remain in the deposit representing a net removal from the atmosphere and from the active hydrologic system in early to middle mars history and forming an accessible record of aqueous conditions and possible biological environments dating from that time

geological and hydrological histories of the argyre province mars the geologic history of the multi ringed argyre impact basin and surroundings has been reconstructed on the basis of geologic mapping and relative age dating of rock materials and structures the impact formed a primary basin rim materials and a complex basement structural fabric including faults and valleys that are radial and concentric about the primary basin as well as structurally controlled local basins since its formation the basin has been a regional catchment for volatiles and sedimentary materials as well as a dominant influence on the flow of surface ice debris flows and groundwater through and over its basement structures the basin is interpreted to have been occupied by lakes including a possible mediterranean sized sea that formed in the aftermath of the argyre impact event the hypothesized lakes froze and diminished through time though liquid water may have remained beneath the ice cover and sedimentation may have continued for some time at its deepest the main argyre lake may have taken more than a hundred thousand years to freeze to the bottom even absent any heat source besides the sun but with impact induced hydrothermal heat geothermal heat flow due to long lived radioactivities in early martian history and concentration of solutes in sub ice brine liquid water may have persisted beneath thick ice for many millions of years existence of an ice covered sea perhaps was long enough for life to originate and evolve with gradually colder and more hypersaline conditions the argyre rock materials diverse in origin and emplacement mechanisms have been modified by impact magmatic eolian fluvial lacustrine glacial periglacial alluvial colluvial and tectonic processes post impact adjustment of part of the impact generated basement structural fabric such as concentric faults is apparent distinct basin stratigraphic units are interpreted to be linked to large scale geologic activity far from the basin including growth of the tharsis magmatic tectonic complex and the growth into southern middle latitudes of south polar ice sheets along with the migration of surface and sub surface volatiles towards the central part of the primary basin the substantial difference in elevation with respect to the surrounding highlands and tharsis and the thaumasia highlands result in the trapping of atmospheric volatiles within the basin in the form of fog and regional or local precipitation even today in addition the impact event caused long term millions of years hydrothermal activity as well as deep seated basement structures that have tapped the internal heat of mars as conduits for far greater time possibly even today this possibility is raised by the observation of putative open system pingos and nearby gullies that occur in linear depressions with accompanying systems of faults and fractures long term water and heat energy enrichment complemented by the interaction of the nutrient enriched primordial crustal and mantle materials favorable to life excavated to the surface and near surface environs through the argyre impact event has not only resulted in distinct geomorphology but also makes the argyre basin a potential site of exceptional astrobiological significance

pervasive aqueous paleoflow features in the aeolis zephyria plana region mars abstract a survey of themis visible wavelength images in the aeolis zephyria plana region over the two western lobes of the equatorial medusae fossae formation mff shows 150 sinuous ridges having a variety of morphologies and contexts to systematize investigation we use a classification scheme including both individual ridge and ridge network types as well as associations with impact craters and fan shaped features the morphology of the ridges their location downslope from higher topography e g crater rims and scarps and their association with fan shaped forms indicate that most sinuous ridges formed through overland aqueous flow analysis of observations by individual ridge type leads to interpretation of most of these sinuous ridges as inverted fluvial channels or floodplains and a few as possible eskers with the origin of the remaining ridges under continuing investigation about 15 of the sinuous ridges are associated with impact craters but data analysis does not support a genetic relationship between the craters and the sinuous ridges instead analysis of one sinuous ridge network associated with a crater indicates that the water source for the network was atmospheric in origin namely precipitation runoff the broad areal distribution of these 150 ridges and the network morphologies in particular the branched and subparallel types suggest that an atmospheric water source is generally applicable to the population of sinuous ridges as a whole this concentration of sinuous ridges is the largest single population of such landforms on mars and among the youngest these ridges are situated at a paleoscarp between cerberus palus and the aeolis highlands suggesting that the precipitation that formed them was orographic in origin the ages of the equatorial mff units in which this population of sinuous ridges is found imply that this orographic rain and or snow fell during some period from the late hesperian through the middle amazonian

amplitudes of orbitally induced climatic cycles and patterns of hominin speciation abstract palaeoanthropologists and archaeologists have long invoked climate change to explain aspects of human evolution collection of new climatic and environmental data combined with new fossil discoveries and methodological improvements continue to make exploration of this link a vital endeavour in studying human evolution the current study employs a global climatic dataset and a rigorously compiled catalogue of hominin first and last appearance dates to test the effects of changes in temperature on hominin speciation and extinction through the use of wavelet analysis and bandpass filters the eccentricity obliquity and precession components of the studied climatic record are extracted and tested independently for associations with patterns of speciation and extinction results suggest that all three components may play a role in speciation events but that only the obliquity cycle shows a statistically significant relationship with extinction events it is suggested that whilst climatic factors could contribute to the appearance of new hominin species subsequent competition between these species may lead to their extinction

volcano ice interactions in the arsia mons tropical mountain glacier deposits fan shaped deposits fsd superposed on the sides of the tharsis montes volcanic edifices are widely interpreted to have been formed by cold based glaciation during the late amazonian a period when the tharsis montes were volcanically active we survey the similar to 166 000 km 2 arsia mons fsd using new high resolution image and topography data and describe numerous landforms indicative of volcano ice interactions these include 1 steep sided mounds morphologically similar to terrestrial tindar that form by subglacial eruptions under low confining pressure 2 steep sided leveed flow like landforms with depressed centers interpreted to be subglacial lava flows with chilled margins 3 digitate flows that we interpret as having resulted from lava flow interaction with glacial ice at the upslope margin of the glacier 4 a plateau with the steep sides and smooth capping flow of a basaltic tuya a class of feature formed when subglacial eruptions persist long enough to melt through the overlying ice and 5 low areally extensive mounds that we interpret as effusions of pillow lava formed by subglacial eruptions under high confining pressure together these eruptions involved hundreds of cubic kilometers of subglacially erupted lava thermodynamic relationships indicate that this amount of lava would have produced a similar volume of subglacial liquid meltwater some of which carved fluvial features in the fsd landforms in the fsd also suggest that glaciovolcanic heat transfer induced local wet based flow in some parts of the glacier glaciovolcanic environments are important microbial habitats on earth and the evidence for widespread liquid water in the amazonian aged arsia mons fsd makes it one of the most recent potentially habitable environments on mars such environments could have provided refugia for any life that developed on mars and survived on its surface until the amazonian

subglacial processes of the scandinavian ice sheet in fennoscandia inferred from flow parallel features and lithostratigraphy abstract subglacial processes of the last scandinavian ice sheet in fennoscandia were investigated on two different scales a detailed case study in southwestern finland and a generalized study in the central parts of the ice sheet previously reconstructed time transgressive glacial flow patterns were correlated with different types of glacial flow parallel features and lithostratigraphic units the comparison of orientations of each flow parallel feature with relative ages of different flow patterns enabled estimations of relative distances of the orientation generating processes in relation to the receding ice margin this method was also used to infer sedimentary environments of each lithostratigraphic facies identified generalized lithostratigraphic sequences were compiled in fennoscandia using sections described previously in areas of ice streams a sandy till showing mature deformation structures forms till sheets drumlins and some ribbed moraines the facies is overlain by occasional glaciofluvial deposits and partly washed deformation till both indicating abundant excess water at the ice bed interface in interlobate areas glaciofluvial material is under and overlain by a silty till showing ductile deformation structures in places uppermost thin clayey till interpreted to be a subglacial melt out till mantles underlying till and subglacial glaciofluvial deposits the characteristics of different units are controlled by ice flow velocities subglacial hydrology and deformation type of the substratum the time transgressive origin of till beds and intervening washed sediment as well as divergent ice flow patterns is emphasized ice flow was concentrated in streams which generated marginal fan shaped lobes interstream areas of low basal velocities and melting rates were left between adjacent ice streams in areas of ice streams fast basal ice flow velocities continuously generated heat and meltwater which flowed at first in the sediment and closer to the margin also in thin discontinuous sheets at the ice bed interface excess water may have subsequently formed a linked cavity system and channelized to a tunnel network initiating esker deposition or incision of tunnel channels most processes operated continuously during deglaciation with spatial and temporal differences in their activity the mode of subglacial drainage changed periodically during deglaciation and was probably controlled by the volume of subglacial meltwater available in some periods sheet flow of basal water deposited major marginal complexes and subsequently tunnel networks were re established esker pattern and sedimentation rates of proglacial varved clays indicate that tunnel drainage of subglacial water was partly episodic

subaqueous outwash deposits in the ingraham ridge chazy new york a 1 5 km segment of ingraham ridge a stratified sand and gravel ridge in northeastern new york is composed dominantly of subaqueous outwash deposits the core of the ridge segment may include subordinate subglacial tunnel deposits the subaqueous outwash is composed mainly of interbedded sediment gravity flow bar dune and ripple deposits that occur in channels sheetlike cross stratified and cross laminated deposits also are common particularly on the distal western margin of the ridge segment the ridge segment is draped by glaciolacustrine laminated sand silt and clay and glaciomarine massive mud westward decrease in grain size and scale of sedimentary structures is attributed to confining ice walls of an asymmetric embayment sediments are deformed in part by the melting of adjacent and buried ice the ridge was modified during champlain sea regression and the reworked deposits were colonized by shallow water organisms reworking may have been minor and the broad low morphology of the ridge

ice marginal sedimentation and its implications for ice lobe deglaciation patterns in the baltic region pohjankangas western finland

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

stratigraphic controls on pool formation in a domed bog inferred from ground penetrating radar gpr ground penetrating radar gpr and terrain conductivity measurements reveal a close correlation between the location of water filled pools and stratigraphic lithologic features in caribou bog a 2200 hectare peatland in central maine the geophysical profiles supported by coring define the general peatland stratigraphy as till underlain by glacio marine sediment overlain by organic rich lake sediment transitioning into terrestrial peat gpr measurements show that open pools coincide with abrupt thinning of lake sediment and glaciomarine clay such that elevated mineral soil surfaces are in direct contact with the base of terrestrial peat the width of these features the gpr reflection patterns the anomalously low terrain conductivity and the core samples obtained support the interpretation of these elevated mineral surfaces as the extension of buried eskers that outcrop on the periphery of caribou bog the geophysical results indicate that two parallel esker ridges are orientated n s and dip towards the south we suggest that the distribution of open pools is related to the distribution of depressions and beads associated with a beaded esker deposit the pools possibly being maintained by local groundwater flow cells associated with the esker gpr and em31 surveys across sphagnum pools defined here as sphagnum filled wet depressions suggest a continuous sequence of underlying lake sediment and glacio marine deposits devoid of elevated mineral surfaces we suggest that sphagnum pools developed after peatland formation secondary features due to changes in water table peat accumulation and or climatic controls q 2005 elsevier b v all rights reserved

glacial dispersal and flow history east arm area of great slave lake nwt canada abstract little work has been completed on paleo ice sheet flow indicators of the laurentide ice sheet west of the keewatin ice divide field mapping sampling and analysis of glaciogenic sediment 500 sample sites in a 33 000 km2 region near the east arm of great slave lake in northwestern canada provided a rare opportunity to improve understanding of sediment erosion and transport patterns glacially eroded bedrock and sedimentary landforms record east to west flow with nw and sw divergence mapped within a portion of the great slave lake flow tract transported till reflects a similar divergent flow pattern based on dispersal geometries for multiple indicators e g heavy minerals and lithic fragments which are aligned with the dominant and latest ice flow direction glaciofluvial erosion e g s forms and till removal transport and deposition mainly as esker sediment are set within 0 3 3 km wide meltwater erosional corridors spaced regularly at 10 15 km intervals transport paths and distances are comparable in till and esker sediment however distances appear to be greater 5 25 km in some esker constituents and indicator minerals are typically more concentrated in esker sediment than in till corridors form a divergent array identical to the pattern of ice flow features the congruence of ice and meltwater flow features is interpreted to be a response to a similar ice sheet gradient and close timing of events late dominant glacial ice flow and meltwater flow the similarity in glacial and glaciofluvial flow patterns has important ramifications for event reconstruction and for exploration geologists utilizing mineral and geochemical tracing methods in this region and possibly other parts of northern canada the correspondence between east arm dispersal patterns landforms and flow indicators supports interpretation of a simple and predictable single flow divergence model this is in contrast to previous multi flow models in which fan shaped geometries are often reported to result from multiple transport events compared to single flow divergence the observed widespread effects of glaciofluvial processes e g erosional corridors indicate a need to update existing terrain process models

sediments and landforms at kviarjokull southeast iceland a reappraisal of the glaciated valley landsystem abstract eyles identified kviarjokull an outlet of the icecap oraefajokull southeast iceland as an exemplar of the glaciated valley landsystem emphasising rockfall debris supply passive transport and reworking of a thick cover of supraglacial morainic till in this paper we take a fresh look at the sediments and landforms of kviarjokull focusing on clast form analysis to reconstruct primary transport pathways new data demonstrate the importance of active transport of debris derived from the glacier bed substantial portions of the supraglacial debris cover can be traced back to englacial channel fill deposits or anomalously thick exposures of basal ice these two types of sediments also make up much of kviarjokull s large neoglacial moraine rampart we attribute the abundance of these non rockfall sediments to the presence of a terminal overdeepening and the switch from predominantly subglacial to predominantly englacial drainage that this induces this hydrological switch enhances retention of debris within ice transport preventing it from being washed away and making it available to feed ice marginal moraine formation the complexity of sediment transport processes observed at kviarjokull and the contrast between it and alpine glaciers undermines any single concept of the glaciated valley landsystem accordingly we propose kviarjokull as the type example of a distinct subclass defined by its moderate relief high debris turnover and drainage behaviour characteristic of an overdeepened basin

sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications an example from anglesey north wales uk subglacial drainage systems exert a major control on basal sliding rates and glacier dynamics however comparatively few studies have examined the sedimentary record of subglacial drainage this is due to the paucity of modern analogues the limited recognition and preservation of upper flow regime deposits within the geological record and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments e g glacier outburst flood deposits within this study the sedimentological and structural evolution of a subglacial to subaerial ice marginal proglacial drainage system is examined particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context facies are attributed to subglacial meltwater activity and record sedimentation within a confined but progressively enlargening subglacial channel system produced under dune to upper flow regime conditions bedforms include rare large scale sinusoidal bedding with syn depositional deformation produced by current induced traction and shearing within the channel margins subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel abandonment or a seasonal drainage regime retreat of the ice margin led to the establishment of subaerial drainage with phases of sheet flow punctuated by channel incision and anastomosing channel development under diurnal ablation related seasonal discharge the presence of extensive hydrofracture networks demonstrate that proglacial groundwater levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

sequence stratigraphy of a glaciated basin fill with a focus on esker sedimentation a large integrated data set of cores outcrop data and seismic transects from the mud buried vars winchester esker in the champlain sea basin canada was studied to gain insight into how muddy glaciated basins fill with sediment and how esker sedimentary systems contribute to this process three stratigraphic units a till sheet over carbonate bedrock the vars winchester esker and overlying champlain sea mud are identified in the data set the till is massive mud rich carbonate rich and drumlinized the esker is also carbonate rich and rests erosively on till or bedrock it consists of two elements a narrow gravelly central ridge and a broad sandy carapace three units comprise the overlying mud package gray carbonate rich rhythmites massive bioturbated mud and carbonate poor red and gray rhythmites a sequence stratigraphic model is proposed to explain these observations emphasis is placed on gradual ice front translation superimposed by rapid meltwater events the esker is interpreted to have been derived from the underlying till by water that flowed through a subglacial conduit r channel within which the narrow gravelly central ridge was deposited most mud and finer sand bypassed the conduit and was deposited proglacially on the floor of the champlain sea first as sandy outwash and farther basinward as muddy carbonate rich rhythmites gradual ice front retreat superposed distal facies over proximal facies generating the upward fining succession that starts with the esker gravel and ends with muddy rhythmites most esker sediment appears to have been deposited during rapid jokulhlaup like floods that punctuated gradual retreat discharges are estimated to have been high possibly on the order of several hundred to perhaps more commonly several thousand cubic meters per second the chaotic and random looking appearance of the resultant sedimentological signatures in the esker sensu stricto is sharply contrasted with the regularity of the muddy rhythmites if the rhythmites are indeed correlative to the esker which seems reasonable given their geochemistry and the fact that their volume scales to the volume of mud in the till the flood events that deposited the esker must have been seasonally mediated and the basin water must have attenuated the flood signal resulting in a rhythmic on off signature in more distal portions of the system the regularity of the rhythmites does not betray the chaotic nature of the esker sensu stricto and vice versa studying either one in isolation would lead to a very different end member impression of how eskers form and how esker sedimentary systems operate during the infilling of glaciated basins

the origin and glaciodynamic significance of sandstone ridge networks from the hirnantian glaciation of the djado basin niger the djado basin niger was located beneath the inner part of the late ordovician ice sheet the felar felar formation consists mainly of glaciomarine deposits associated with the major ice sheet recession within the glaciation and is bounded by two glacial unconformities structures corresponding to sandstone ridges are found within the felar felar formation sandstone ridges are several metres high about 10 m wide and hundreds of metres long these structures are organized in extensive anastomosed to subpolygonal networks the association of sandstone ridge networks with the later glacial unconformity and with other glacial evidence suggests sub glacial conditions for their origin sandstone ridge sedimentological characteristics indicate that sandstone ridges result from the scouring of the felar felar formation by sub glacial turbulent and pressurized meltwater then subglacial cavities were infilled with sand derived from glacial abrasion sandstone ridge networks are comparable with tunnel channels and document unusual drainage structures of the inner part of the palaeo ice sheet

inverted fluvial features in the aeolis zephyria plana western medusae fossae formation mars evidence for post formation modification 1 the aeolis and zephyria plana contain the western most portion of the medusae fossae formation mff an enigmatic and extensive light toned deposit located in the martian equatorial region and dated from the hesperian to amazonian epochs this area hosts a large population of sinuous ridges srs interpreted as inverted fluvial features formed by precipitation indurated by chemical cementation buried by subsequent deposition and finally exhumed this interpretation of srs as uniformly fluvial represents a modification to an earlier hypothesis for one particular sr of possible glaciofluvial i e esker formation these srs provide a tool to investigate the degree and character of post fluvial modification processes in this region we combined digital terrain models made from context camera ctx and high resolution imaging science experiment hirise stereo image pairs with individual data points from the mars orbiter laser altimeter mola to estimate relief cross sectional profiles longitudinal profiles and slope directions of selected srs longitudinal profiles of several srs display undulations with amplitudes of up to order 100 m while some of the lower amplitude undulations may be due to differential erosion undulations having amplitudes in excess of sr relief require alternative explanations our combined morphologic and topographic analysis suggests that multiple post flow processes including compaction of the deposits and tectonic displacements have modified the original sr profiles specification of the type s and magnitudes of these modification processes will contribute to understanding both the potential of post flow modification of fluvial profiles elsewhere on mars as well as the nature and properties of the mff