the origins of s forms form similarity process analogy and links to high energy subglacial meltwater flows abstract this paper first presents the history of ideas on s form formation with an emphasis on meltwater models the main approach is based on form similarity between modern erosional marks and subglacial s forms form similarity is then extended to process similarity which promotes understanding of s forms three classes of erosional marks are identified obstacle scours basin shaped erosional marks and landforms related to escarpment flow identification is based on form with recognition of elements though it mainly depends on recognition of the whole form in much the same way as we recognize family members or familiar flowers flow conditions related to the various flow features are determined by flow visualization and computational fluid dynamics some s forms are produced in flume models though most are natural features observed in the field examples from beneath past ice sheets are seen in the field and illustrated by air and ground photographs satellite images and dem digital elevation model the results of this work show remarkable similarity between modern erosional marks and ancient subglacial s forms consequently established processes are attributed to ancient forms in turn s forms may be used abductively to interpret subglacial hydrological conditions the lack of waning stage bedforms scoured into primary forms suggests that erosional marks form under abruptly terminating catastrophic flow

reply to comment by o cofaigh dowdeswell king anderson clark dja evans j evans hindmarsh lardner and stokes comments on shaw j pugin a young r 2009 a meltwater origin for antarctic shelf bedforms with special attention to megalineations geomorphology 102 364 375 0169 555x see front matter 2009 elsevier b v a doi 10 1016 j geomorph 2009 12 008 andre pugin s name does not appear on this reply because there was a delay in our receiving the comment and we responded to a tight deadline unfortunately this left insufficient time for an internal review required by the geological survey of canada before andre could be an author we expected that therewould be a reaction to our paper and serious questions after all we applied controversial ideas to a part of the globe for which we have no first hand experience indeed the observations of king et al 2009 on lineations beneath the rutford ice stream do present a serious challenge to the megaflood hypothesis otherwise our proposals for the formation of subglacial bedforms stand up well to the criticism by cofaigh et al they agree with us that meltwater action was significant to seascape evolution in antarctic shelf crossing troughs and in this respect we gave full credit to their research in many citations however in contrast to our megaflood hypothesis minimal meltwater supply and transfer were central to many earlier models of meltwater in troughs since the volumes of running water in minimal models are negligible shaw et al fig 6 meltwater in these models could have contributed little to seascape evolution much of this reply concerns questions that have been asked repeatedly over the last twenty years especially those concerning a meltwater origin for drumlins we respond emphatically to these questions which have become less not more discerning with time this reply follows the order of the comment and in places simply responds to a particular comment why is it more important that shelf crossing troughs would have been the preferred routes for ice streams surely this assertion prejudges the relative importance of ice streams and meltwater in the formation of bedforms

comment on how plausible are high frequency sediment supply driven cycles in the stratigraphic record by s castelltort and j van den driessche 2003 sedimentary geology 157 3 13

erosion of bedrock by subglacial meltwater cantley quebec several erosional forms on bedrock at cantley quebec differ from well known glacial abrasion forms the forms consist of obstacle marks hollows depressions and channels which are defined by sharp rims smooth inner surfaces divergent flow features and remnant ridges these forms are found on lee lateral and overhung rock surfaces this assemblage of features is best explained by differential erosion produced by separation eddies along lines of reattachment rapid sediment laden turbulent subglacial melt water flows likely produced the forms by corrasion and cavitation erosion sculpted fluvial forms in terrain subject to flooding in australia are identical to some of the cantley forms which confirms their formation by water erosion although glacial abrasion may not be eliminated as an explanation for sculpted forms it is not necessary ice abrasion forms such as striations and such plucked forms as gouges and crescentic fractures are also present at the cantley site pitted forms polishing and carbonate precipitate are also found the occurrence of abrasion pitting polishing and carbonate precipitate with meltwater forms suggests that the meltwater flows were subglacial decoupling of abrading ice from its bed temporarily suspended glacial abrasion whereas reattachment of ice to the bed may have led to the rounding of sharp edges and the production of striations superposed on the glacifluvial forms the association of forms produced both by glacifluvial erosion and ice abrasion suggests that the glacier was alternately lifted from and reattached to the bed during periodic subglacial floods these floods may have affected the dynamics of the ice sheet and depositional sequences related to catastrophic meltwater outbursts probably were laid down in adjacent basins

thin film channelized drainage or sheetfloods beneath a portion of the laurentide ice sheet an examination of glacial erosion forms northern new york state usa abstract morphologic analyses of characteristic bedrock erosion forms found in northern new york state usa were used to reconstruct the subglacial conditions under which they may have been produced observations from sites on wellesley island n y at point salubrious n y and at an open pit mine near balmat n y were combined with regional mapping of a diverse suite of glacial erosion forms in order to establish the areal extent and significance of subglacial drainage in northern new york results of these site specific and regional studies are the basis for discussion of the probable role of subglacial meltwater in the region bedrock erosion forms preserved at various locations in northern new york are interpreted as products of flow separation of localized subglacial meltwater during ice bed decoupling the regional distribution of these forms indicates that they are largely restricted to pre existing subglacially modified bedrock valleys that served as subglacial tunnel channels regionally extensive deep subglacial meltwater flow characterized as sheetfloods is not required to account for the erosional features described from specific sites in northern new york state

regional reconstruction of subglacial hydrology and glaciodynamic behaviour along the southern margin of the cordilleran ice sheet in british columbia canada and northern washington state usa abstract subglacial landsystems in and around okanagan valley british columbia canada are investigated in order to evaluate landscape development subglacial hydrology and cordilleran ice sheet dynamics along its southern margin major landscape elements include drumlin swarms and tunnel valleys drumlins are composed of bedrock diamicton and glaciofluvial sediments their form truncates the substrate tunnel valleys of various scales km to 100s km length incised into bedrock and sediment exhibit convex longitudinal profiles and truncate drumlin swarms okanagan valley is the largest tunnel valley in the area and is eroded 300 m below sea level over 600 m of late wisconsin age sediments consisting of a fining up sequence of cobble gravel sand and silt fill okanagan valley landform substrate relationships landform associations and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds they are best explained by meltwater erosion and deposition during ice sheet underbursts during the late wisconsin glaciation okanagan valley functioned as part of a subglacial lake spanning multiple connected valleys few 100s km of southern british columbia subglacial lake development started either as glaciers advanced over a pre existing sub aerial lake catch lake or by incremental production and storage of basal meltwater high geothermal heat flux geothermal springs and or subglacial volcanic eruptions contributed to ice melt and may have triggered along with priming from supraglacial lakes subglacial lake drainage during the underburst s sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys progressive flow channelization focused flows toward major bedrock valleys in okanagan valley most of the pre glacial and early glacial sediment fill was removed a fining up sequence of boulder gravel and sand was deposited during waning stages of the underburst s and bedrock drumlins in okanagan valley were enhanced or wholly formed by this underburst s subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes the prevailing conceptual model for growth and decay of the cis suggests significantly thicker ice in valleys compared to plateaus subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner due to melting and enhanced sliding with significant transfer of ice toward the ice sheet margin subglacial lake drainage may have hastened deglaciation by melting ice lowering ice surface elevations and causing lid fracture this paper highlights the importance of ice sheet hydrology its control on ice flow dynamics distribution and volume in continental ice masses

a depositional model for rogen moraine with examples from the avalon peninsula newfoundland rogen moraine is explained by subglacial meltwater processes through a form analogy between moraine ridges and ripples produced on the underside of river ice this mechanism for rogen moraine formation is compatible with the meltwater hypothesis for drumlins a unified explanation for rogen moraines and drumlins is attractive and necessary because they are part of a continuum the meltwater hypothesis is tested on rogen moraine of the avalon peninsula newfoundland mapping shows that ice and meltwater flowed northeastwards from st mary s bay and fanned out across the peninsula the sedimentology of four moraine ridges and one moraine hummock favours deposition in subglacial cavities sediment in the ridges travelled only short distances and there is abundant evidence of water sorting and deposition from debris flows bedding within ridges conforms with surface slopes and clast fabrics relate to local morphology rather than to the regional ice flow direction additional sedimentary observations from qu

subglacial erosional marks wilton creek ontario a variety of p forms are discussed in terms of the agent producing them a general conclusion based on form and the location of striations relative to p forms is that they are produced by meltwater rather than ice erosional marks in the wilton creek valley ontario are different from earlier described p forms their relationship to striations establishes them as being of subglacial origin and their form similarity with flutes together with the partial or total absence of striations on them suggests a fluvial origin large scale forms are interpreted as spindle shaped flutes associated with flow separation small scale forms are subdivided into straight spindle forms curved spindle forms braided forms and scallops they appear not to have followed the inverse relationship between size and flow velocity reported for some other erosional marks potential but speculative explanations for these small scale forms are that they are related to taylor gortler vortices vortices on mixing layers or trailing

hairpin erosional marks horseshoe vortices and subglacial erosion abstract crescentic erosional marks wrapped around obstacles and extending into straight grooves are termed hairpin erosional marks they are u shaped to semi circular in cross section are deepest around the upstream shoulders of the obstacles and range over seven orders of magnitude in scale some are asymmetrical with one groove better developed than the other the straight grooves may broaden and shallow rapidly in the downflow direction upstream grooves merge with rather than cross downstream crescentic marks grooves are distinct from glacial abrasion forms and many are not striated hairpin erosional marks are interpreted as being products of scour by horseshoe vortices in turbulent fluids this interpretation is supported by the close similarity of these marks to scours produced experimentally and in nature by horseshoe vortices estimated reynolds numbers show that such vortices are probable around obstacles in wind and flowing water but are extremely unlikely in ice aeolian hairpin erosional marks related to yardangs are illustrated to support this conclusion the surface texture cross sectional shapes and spatial patterns of hairpin erosional marks also discount formation by ice a model for the evolution of isolated erosional drumlins from an initial field of hairpin erosional marks extends earlier research on a meltwater hypothesis for drumlins

evidence of glacial abrasion in the calingasta uspallata and western paganzo basins mid carboniferous of western argentina abstract evidence of glacial abrasion is present in the basal part of the carboniferous section of the calingasta uspallata and paganzo western argentina where subglacial and proximal glacial marine diamictites with pebbly dropstone shales constitute the dominant facies association intraformational striated pavements are exposed in the hoyada verde and leoncito formations of the calingasta uspallata basin marine invertebrate fossils levispustula zone in associated shales indicate a mid carboniferous age for both units a single layer striated boulder pavement is superbly exposed in the hoyada verde formation local a axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement paleo ice flow directions have an nne ssw strike the leoncito intraformational pavement is shaped on bioturbated fine grained sandstones with plant remains glacial striations are straight and parallel with subcircular cross sections dome like features are present in the surface which is covered in turn by a sandy bouldery diamictite four striated surfaces are present in the western paganzo basin three of them pavements at the san juan river valley loma de los piojos and agua hedionda are developed on basement rocks they contain parallel to subparallel striations nailhead striations crescentic gouges impact marks and furrows the pavements are overlain by thin up to 1 5 m laterally discontinuous diamictite beds with striated clasts some of them bullet shaped paleo ice flow directions are n ne directed an intraformational pavement is also present at the san juan river valley section it is carved on the top of the basal diamictite and exhibits furrows probably caused by subglacial soft sediment grooving the dispersion of paleo ice flow directions in the calingasta uspallata and paganzo basins indicates i regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions ii glacial erosion by ice grounded below sea level and confined to the margins of the basins

flow dynamics and till genesis associated with a marine based antarctic palaeo ice stream geophysical and geological data indicate that during the last glacial cycle a palaeo ice stream drained the antarctic peninsula ice sheet apis through marguerite bay to the edge of the continental shelf via a bathymetric trough marguerite trough mega scale glacial lineations msgl in outer marguerite trough are formed in an acoustically transparent sediment unit consisting of a soft deformation till the association of msgl with deformation till indicates that bed deformation occurred beneath the ice stream and the thickness of the subglacial deforming layer was on the order of several metres msgl within outer marguerite trough are related to a pre existing thick sequence of soft sediments on the outer shelf and are inferred to have formed by a combination of subglacial sediment deformation by attenuation from a point source and groove ploughing morphologically the msgl differ in several respects from those documented elsewhere and this variation suggests a polygenetic origin for this subglacial landform an initial advance of the apis across the marguerite bay continental shelf at the lgm deposited a stiff subglacial till following this advance the ice margin within marguerite trough retreated 70 100 km before stabilising and depositing a grounding zone wedge an ice stream then developed in the trough and extended to the shelf edge forming a soft deformation till development of the ice stream may have been a glacio dynamic response to regional deglaciation subsequent retreat of the marguerite trough ice stream was underway by 13 490 uncorrected 14c years before present based on the geophysical and core data ice stream retreat appears to have been rapid and it contrasts with reconstructions of palaeo ice streams from other locations in antarctica this implies marked regional variations in antarctic ice stream dynamics during late quaternary deglaciation

drumlin formation related to inverted melt water erosional marks drumlin forms are described from maps and air photographs of a part of the athabasca plains northern saskatchewan three major forms spindle parabolic and transverse asymmetrical are recognized these forms which may show superimposed minor elements depart from classical descriptions of drumlins but are similar to moulds of erosional marks created by separated fluid flows assemblages of drumlins also show characteristics similar to those of erosional marks the form analogy between drumlins and moulds of erosional marks is carried to a conclusion that drumlins may be formed by the infilling of erosional marks created on the under side of glaciers by separated subglacial melt water flows estimates of specific discharge are obtained by means of an expected range of reynolds number geomorphological evidence is given for large scale erosion by subglacial melt water a discussion of the sedimentology stratigraphy and deformational structure of the interiors of drumlins shows that they may be explained by the erosional mark hypothesis this paper emphasizes the importance of melt water as a geomorphic agent and may have broad implications for ice sheet dynamics and profiles rates of deglaciation and the occurrence of bedrock thrusting by ice

controlling mechanism of local scouring experimental study of clear water scouring around a circular cylinder shows that the scour mechanism is coupled to the three dimensional separation of the upstream boundary layer and the periodic vortex shedding in the wake of the cylinder the first scour appears in the wake of the cylinder the main scouring agent in the upstream region is a system of horseshoe vortices the vortices have a periodical character that causes a triple scour profile to develop in the upstream region during scouring the number and periods of horseshoe vortex shedding undergo no appreciable change despite the clear water stage the transport phenomenon is periodical transport of sediment takes place through turbulent scales of comparable size to macro length scales the size of horseshoe vortices are representative for the macroscale wake scouring is caused by the primary wake vortices and the accelerated side flow the process is characterized by a strong periodical transport and the formation of ripples the periodicity is controlled by the shedding frequency of the wake vortices collars attached to the cylinder cannot prevent the formation of the vortices

drumlins and catastrophic subglacial floods shaw j kvill d and rains b 1989 drumlins and catastrophic subglacial floods in j menzies and j rose editors subglacial bedforms drumlins rogen moraine and associated subglacial bedforms sediment geol 62 177 202 a number of lines of evidence are shown to be consistent with drumlin formation by catastrophic meltwater floods drumlins are associated with landforms related to such floods and landscapes produced by outburst floods in extragiacial areas contain drumlin like landforms some drumlins which contain mainly residual materials are compared to similar forms covering a wide range of scales and are interpreted to be scour remnant ridges produced by the action of horseshoe vortices on subgiacial materials these vortices are a product of flow separation in turbulent fluids and this interpretation implies drumlin formation by meltwater other drumlin calied cavity fill drumlins have distinctive shapes that are analogous with infilled erosional marks produced by turbulent separated flows these drumlins are interpreted as the infills of cavities eroded upwards into glacier beds by broad subgiacial meltwater sheetflows the sedimentology and internal structure of the cavity fill drumlins indicate rapid deposition from hyperconcentrated flow clast shape surface texture and lithology are consistent with the short distance of giaciofhivial transport predicted by the cavity fill hypothesis estimates of flow discharge 0 6 6 x 107 m3 s total volume of flow 84 1 103 km3 and flow duration 16 162 days are given for the catastrophic flood proposed to have produced the livingstone like saskatchewan drumlin field subgiacially derived floods are used to explain the sudden drainage of extraglacial lakes and major depositional events in proglacial lakes and it is suggested that they might have contributed to the lid of cold freshwater over the north atlantic held to have caused a late glacial cooling event the flood hypothesis requires extensive subgiacial lakes to have occurred beneath the laurentide and fennoscandian ice sheets which if they existed must have influenced the form and behaviour of these major bodies of ice

a glaciofluvial origin for drumlins of the livingstone lake area saskatchewan the livingstone lake drumlin field of northern saskatchewan is on the athabasca plains it is draped over high ground underlain by the precambrian athabasca sandstone the drumlins occur in spindle parabolic and transverse asymmetrical forms a map of individual drumlins shows that features of similar form occur together the drumlins are related on a regional scale to even larger landforms there is also an arrangement of drumlins in streams parallel to the assumed flow direction these patterns illustrate spatial organisation of the drumlin forming flows the livingstone lake drumlins are closely related to tunnel valleys large crescentic scours and eskers exposed bedrock reveals widespread scalloping and sichelwannen an argument is made that drumlins are related to these glaciofluvial forms but were created at different times and by different flows than those forming small scale flutings and other lodgment features sediments within the drumlins are mainly primary water sorted deposits some of wh

erosion of bedrock by subglacial meltwater georgian bay ontario a regional view a spectacular series of sculpted erosional forms s forms is mapped and described from a 70 km wide area along the shore of georgian bay ontario which except for a scattered boulder lag has been swept clean of sediment a great variety of sculpted forms is described and illustrated and grouped into three classes transverse longitudinal and nondirectional forms transverse forms comprise transverse troughs muschelbruche sichelwannen and comma forms longitudinal forms comprise spindle flutes cavettos and furrows and nondirectional forms consist of undulating surfaces and potholes transverse forms are preferentially located on stoss slopes and longitudinal forms on lee slopes of rock rises undulating nondirectional forms are found on distal slopes and potholes at major breaks in slope this correlation of form and bed topography suggests that relief exerts considerable control on both form and location form geometry is also inferred to be related to coherent flow structures and their int

a flowline map of glaciated canada based on remote sensing datathis paper is accompanied by a large foldout map entitled a flowline map of glaciated canada based on remote sensing data see pocket on back cover the map a flowline map of glaciated canada based on remote sensing data presents flowlines for the former laurentide and cordilleran ice sheets based on flow indicators derived from aggregated flo

drumlin formation by subglacial meltwater erosion some drumlins are shown to belong to a family of remnant erosional ridges associated with subglacial meltwater the lengths of these ridges vary in scale from a few tens of millimetres to over 5 km similar form elements are illustrated for three scales of forms it is concluded that some drumlins are composed of preexisting sediment or bedrock left upstanding in ridges as a result of the removal of surrounding materials this erosional theory is related to an earlier theory in which drumlins are held to result from the infilling of subglacial cavities the unifying factor for both theories is the role of sheets of subglacial meltwater

temporal changes in subglacial meltwater activity field evidence from the late devensian in the north of ireland abstract temporal changes in meltwater abundance distribution and characteristics controlling subglacial processes and ice sheet dynamics can be inferred from subglacial sediment successions field evidence for changes in subglacial meltwater characteristics over time is presented from two sites doonan drummee near a former late weichselian devensian ice centre in the north of ireland on a macroscale both sites investigated show subglacial diamicton overlying glacially planated bedrock platforms in more detail primary sedimentary structures and facies variability show a complex relationship between depositional processes and meltwater characteristics at the ice bed interface ibi sedimentary evidence suggests sediment transport and deposition took place by low viscosity subglacial slurries mobile sediment meltwater admixtures which are part of a continuum between the processes of subglacial sediment deformation and subglacial meltwater flooding subtle changes in meltwater abundance and distribution at the ibi controlled slurry rheology mechanisms of particle support and detailed sediment depositional processes

quaternary stratigraphy and history of the ootsa lake cheslatta river area nechako plateau central british columbia erosion along the nechako reservoir and cheslatta river spillway has resulted in unusually well exposed late quaternary and holocene stratigraphy surficial sediments in the study area are mostly products of late wisconsinan glaciation however evidence for pre late wisconsinan sedimentation has been found along the shores of the nechako reservoir including till of an older glaciation and organic bearing blue grey lacustrine sediments of probable middle wisconsinan age stratigraphic correlation of the lake sediments suggests that an extensive lake system occurred in the region during the olympia nonglacial interval late wisconsinan ice initially moved along major valleys with glaciofluvial outwash deposited in front of the advancing ice advance phase glaciolacustrine sediments are rare but significant as slope failures are spatially associated with areas where they are preserved the distribution of these sediments and associated deltaic deposits indicates that advance phase glacial lakes occurre

ice sculpture in the martian outflow channels many landforms in martian outflow channels have characteristics that suggest sculpture by glaciers ice streams or ice sheets viking orbiter and terrestrial satellite images were examined at similar resolution to compare features of the martian outflow channels to features produced by the movement of ice on earth many resemblances were found they include the anastomoses sinuosities and u shaped cross profiles of valleys hanging valleys and linear scour marks on valley walls grooves and ridges on valley floors and streamlining of bedrock highs the question of whether ice could have moved in the martian environment is investigated since gradients on martian channel floors are extremely low or even reversed a certain thickness of ice is required to initiate glacial motion if ice filled the martian channels to the level of interior plateaus flow could have occurred even under present climatic conditions although warmer climates in the past would have been more favorable additionally if the channel fluids were brines ice might have been wet based and would have moved readily by slipping over the ground it is envisioned that springs or small catastrophic outbursts discharged fluids from structural outlets or chaotic terrains the fluids built icings that may have grown into substantial masses and eventually flowed like glaciers down preexisting valleys alternatively the fluids may have formed rivers or floods that formed ice jams and consolidated into icy masses in places where obstacles blocked their flow these masses of ice or slush were probably episodic and temporary but where they occurred within the channels they may have produced landforms that are characteristic of glacial sculpture on earth

a numerical study of thermal and chemical structures at the core mantle boundary abstract the core mantle boundary cmb represents the lower boundary layer of the actively convecting earth s mantle and is structurally very complex thermal and chemical structures such as thermal plumes and thermochemical piles have been considered to explain the complexities both affect the dynamics of the earth s mantle and its temporal evolution but also the surface plates are an essential aspect of mantle convection that strongly influence the dynamics of the interior we use numerical thermochemical models of mantle convection to study the structure and dynamics of the lowermost mantle our approach allows for the investigation of plumes and piles in combination with plate like surface motion and deep subduction the models show that the presence of a dense cmb layer generally reduces the mobility of the surface plates but that during plate evolution a variety of plume classes occur leaving a complex structure at the cmb the cmb topography shows large elevated areas with sharp edges and a flat or slightly dented top for piles with plumes atop also plume clusters can cause large elevated areas with sharp edges but a flat top with a few smaller peaks smaller scale patterns often close to the edges of the large structures cause smaller peaks in cmb topography and can be explained by either line plumes or wind driven thermals the latter often arise when heat is trapped beneath subducted slabs that spread over the cmb

drumlins subglacial meltwater floods and ocean responses drumlins and erosional marks in bedrock give evidence for broad subglacial meltwater floods that have discharge rate estimates of about 10 6 m 3 s similar discharge rates are obtained for other late glacial catastrophic floods the total volume of meltwater that is thought to have formed the livingstone lake saskatchewan drumlin field is estimated at 8 4 x 10 4 km 3 this volume is equivalent to a eustatic rise of 0 23 m in global sea level meltwater release and roughly contemporaneous formation of drumlin fields in north america and europe could have involved several metres of sea level rise in a few years the implications of such floods for the generation of myths and the interpretation of the oxygen isotopic record of the oceans are discussed high meltwater discharges are of potential importance to the generation of a lid of cold fresh water over the north atlantic and its effects on late glacial climate

the origin of the western lake erie grooves ohio implications for reconstructing the subglacial hydrology of the great lakes sector of the laurentide ice sheet abstract streamlined grooves and s forms cover the western lake erie islands ohio as well as the channels between the islands and the adjacent mainland although previous interpretations advocate direct glacial ice erosion we offer the alternative interpretation that forms were eroded by meltwater specifically by plucking sediment abrasion and cavitation in high velocity sediment laden flows we base our arguments on detailed descriptions and interpretations of the glacial grooves state memorial site ggsm on kelleys island the site consists of a linear furrow that is adorned by s forms in its base and on its walls these include linear forms cavettos sichelwannen comma forms multi troughed forms and plunging forms all s form sites provide a snapshot of the last phase of erosion after evolution of the local landscape through multiple generations of s form formation as s forms are found on topographic highs and lows we believe they represent a regional flow that overtopped the majority of the islands flow was initially as a sheet that quickly collapsed into channelized flow that was diverged around the islands we also believe that this flow had a major impact on the laurentide ice sheet in this region resulting in rapid glacial advance and extremely low ice sheet profiles

the role of meltwater in glacial processes abstract water plays a dominant role in many glacial processes and the erosional depositional and climatic significance of meltwaters and associated fluvioglacial processes cannot be overemphasized at its maximum extent c 20 000 years ago the volume of the laurentide ice sheet was 33 106 km3 about the same as the volume of all ice present today on planet earth the bulk of this was released as water in little more than 10 000 years pulses of meltwater flowing to the atlantic ocean from large ice dammed lakes altered thermohaline circulation of the world s oceans and global climate one such discharge event via hudson bay at 8200 years bp released 160 000 km3 of water in 12 months global sea levels recovered from glacial maximum low stands reached at about 20 000 years ago at an average rate of 15 m per thousand years but estimates of shorter term rates suggest as much as 20 m sea level rise in 1000 years and for short periods rates as high as 4 m per hundred years meltwaters played a key role in lubricating ice sheet motion and thus areal abrasion across the inner portions of the ice sheet where it slid over rigid crystalline bedrock of the canadian shield the recharge of meltwater into the ice sheets bed was instrumental in generating poorly sorted diamict sediments till by sliding induced shearing and deformation of overpressured sediment and soft rock the transformation of overpressured till into hyperconcentrated slurries in subglacial channels may have generated a highly effective erosional tool for selective overdeepening and sculpting of bedrock substrates some workers credit catastrophic subglacial megafloods with the formation of drumlins and flutes on till surfaces subglacial melt river systems were instrumental in reworking large volumes of glaciclastic sediment to marine basins it has been estimated that less than 6 of the total volume of glaciclastic sediment produced during the pleistocene remains on land fluvioglacial and glaciolacustrine sediments and landforms dominate large tracts of the glacial landscape in north america the recharge of subglacial meltwater into underlying bedrock and sediment aquifers created transient reversals in the long term equilibrium flow directions of basinal fluids with regard to pre pleistocene glacial record meltwaters moved enormous volumes of terrestrial glaciclastic sediment to marine basins and thus played a key role in preserving a record of glaciation a record otherwise almost entirely lost on land

evidence for abundant subglacial meltwater beneath the paleo ice sheet in pine island bay antarctica marine geological and geophysical data collected from the continental shelf in pine island bay antarctica reveal a complex paleo subglacial drainage system controlled by bedrock topography and subglacial meltwater discharge significant amounts of freely flowing meltwater existed beneath former ice sheets in pine island bay subglacial drainage is characterized by descriptions of glacial landforms imaged on the sea floor and sedimentary deposits collected in piston cores bedrock geology is characterized using seismic data large scale landforms on the shelf include channels and cavities incised into impermeable crystalline bedrock there is a transition from randomly oriented channels on the inner shelf to a dendritic pattern of elongate channels on the middle shelf on the outer shelf a change in basal conditions occurs where sedimentary deposits bury crystalline bedrock no evidence for flowing meltwater exists on sedimentary substrates instead meltwater formed a the ice sediment contact was incorporated into the sediments contributing to development of a deforming lied which was sampled in piston cores characterization of subglacial meltwater processes that occurred in the past may aid in understanding the role meltwater plays in stability of the west antarctic ice sheet today

glacial abrasion and sliding their dependence on the debris concentration in basal ice a model of bedrock abrasion by a temperate glacier is developed that takes into account the significant impeding effect of scattered rock fragments at the ice rock interface on glacier sliding an increase in the debris concentration above a relatively low value can reduce the abrasion rate by decreasing both the flux of rock fragments and the effective forces which press fragments against the bed abrasion of a simple wavy bed is shown to be most rapid for a relatively low debris concentration above which the abrasion varies inversely with the debris content a similar concentration dependence of abrasion is expected for beds of arbitrary geometry but low roughness sliding glaciers will tend to abrade until the basal ice is nearly stagnant at which point rocks of all sizes start to lodge against the bed

subglacial imprints associated with the isolation and decay of an ice mass in the lower lough erne basin co fermanagh nw ireland high resolution chirp sub bottom profiler and side scan sonar data record the final phases of ice margin activity in the lower lough erne basin at the end of the last cycle of quaternary glaciations in ireland relative to the terrestrial glacial landforms the features in the lough are smaller in scale and are considered to represent local ice mass dynamics that followed regional scale events four phases are identified 1 after the last ice sheet wide readvance associated with the killard point stadial between 15 0 and 14 1 14 c ka bp stagnation zone retreat resulted in isolation of a residual ice block in the lower lough erne basin 2 proglacial waters developed coeval with retreat of the western margin of the ice block drawdown induced localized surging and the generation of push features and lineations 3 squeeze up features reflecting a heavily crevassed ice margin mark the quiescent phase of the local surge cycle 4 iceberg grounding pits and keel marks record calving and rapid disintegration of the lough erne ice margin the well preserved glacigenic features observed in the lake basin suggest formation by a succession of mechanisms that were too short lived to obliterate the underlying evidence of ice margin dynamics

les formes et les marques de l erosion glaciaire du plancher rocheux signification terminologie illustration abstract glacial erosion is characterized by a grain by grain abrasion of the bedrock or the removal of very small fragments which results in a polish or scratches varying in size it may also weaken the rock by fracturation and leave a train of crescentic fractures or shape quarried lee forms differential erosion is also involved since the glacier bed is made of more or less resistant rocks and that the action of glacial flow varies in time and in space so the kind of forms varies hollows worked like grooves or protruding forms like veins if the rock encloses hard cores glacial scouring is downstream in the case of striations or concave chattermarks and upstream in the case of quarried walls the scale may be larger when a protuberance shaped by ice flow becomes an unsymmetrical rock so called roche moutonnee and glacial carving may affect such a form on all sides in a single primary effect the authors aim is to present a qualitative and quantitative hierarchical classification of terms of these minor forms and marks as to better evaluate the morphological results of ice flow erosion on bedrock

antarctic ice streams and outflow channels on mars new sonar images of the antarctic sea floor reveal mega scale glacial lineations that are strikingly similar to longitudinal flutes in martian outflow channels the analogs suggest that ice moved through the martian channels in places and carved the flutes the ice in martian channels may have moved like antarctic ice streams on deformable debris saturated with water under high pore pressure on mars water at the base of ice filled channels may have come from residual water or melt water liberated during past warmer climates or higher heat flows

subglacial meltwater origin and subaerial meltwater modifications of drumlins near morley alberta canada abstract drumlins in the bow valley west of calgary alberta are interpreted as the product of subglacial and subaerial meltwater erosion on the sides of the bow valley highly elongated streamlined first generation drumlins are aligned in an en echelon fashion and are not significantly modified by post glacial processes in the valley bottom scalloped stubby irregularly spaced second generation drumlins are found in close association with valley fill the drumlins are composed of bedrock and diamicton and some are overlain by a thin gravel veneer stratified gravel is found on the leeward flanks of some second generation drumlins meltwater erosional forms s forms found on the limestone bedrock up flow of the drumlins and crescentic furrows around their proximal ends indicate that subglacial meltwater beneath the bow valley ice was probably the main erosive agent responsible for the shaping of the drumlins the second generation drumlins are believed to be the remnants of the first generation drumlins that were dissected and reworked by postglacial subaerial meltwater flow s meltwater drainage from ice dammed glacial lake kananaskis and possibly other glacially dammed tributary valley lakes resulted in the deposition of megaripples 3 5 m high 40 m wavelength 8 km down flow from the drumlins and reverse eddy deposits on the flanks of the drumlins post glacial bow river incision and terrace development has continued to further sculpt these forms

kinematic indicators in fault gouge tectonic analog for soft bedded ice sheets abstract polished slip planes resulting from basin and range detachment faulting of mid tertiary volcaniclastics are well exposed at lake pleasant arizona u s a slip planes show erosional features formed by abrasion below moving sheets of gouge coarse grained diamict during repeated faulting and shearing tectonically generated forms are identical to those found in glaciated terrains slip planes show rat tail ridges and grooves ridge in groove structures nail head striations and wear tracks a prominent morphological element consists of flute ridges up to 30 cm wide and at least 7 m long formed of gouge preserved in the lee of boulders projecting as obstacles above slip surfaces crescentic scours around the stoss side of such boulders record enhanced abrasion by streams of gouge debris clasts are striated and show shapes comparable to flat iron clasts produced by glacial abrasion kinematic indicators at lake pleasant are directly comparable in form to flutes and drumlins in glaciated terrains the data presented here not support a recent hypothesis arguing that glacial striations flutes and drumlins are the product of turbulent subglacial meltwater instead diamict produced along fault planes gouge by low grade shearing is directly comparable to diamict facies deformation till formed by pervasive shear at the base of soft bedded ice sheets both facies are tectonically generated cataclastites produced in low grade shear zones and display genetically related but differently scaled streamlined bedforms

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd

evidence for large scale subglacial meltwater flood events in southern ontario and northern new york state flow line patterns constructed from the orientation of drumlin long axes are used to infer two major subglacial meltwater floods in southern ontario and northern new york state in this interpretation the flood waters of the first event the algonquin surged southward in the later ontarian event powerful floods streamed southwestward along the basins of lakes ontario and erie bedrock fluting upstream pointing noses on escarpments and tunnel channels give supporting evidence for the regional flood hypothesis regional distributions of drift thickness may be explained by this hypothesis