the stratigraphic and sedimentological significance of late devensian ice sheet surging in holderness yorkshire u k amino acid analyses of marine mollusc valves show that the basement till of holderness yorkshire is of late devensian age ca 20 000 bp and not pre ipswichian 125 000 bp as is traditionally supposed together with the overlying skipsea and withernsea tills the basement till is argued to be a deformation till resulting from the repeated onshore surging of late devensian ice over a muddy sea floor and the subglacial transport attenuation and mixing of marine sediment silts on the surface of the basement till yielding 14c dates of 18 500 and 18 240 bp have been regarded as minimum ages for late devensian glaciation in eastern england e g the dimlington stadial of rose 1985 1989 the amino acid data presented here indicates that the maximum of the late devensian glaciation in eastern england occurred earlier sedimentological interpretation of the late devensian tills of holderness as glacially reworked marine sediments supports previous glaciological models of the british ice sheet involving surging of ice lobes along the coast of eastern england the basement skipsea and withernsea tills are separated by shallow marine sediments and may be representative of deformable bed till facies deposited below pleistocene ice sheets moving over soft fine grained sediments

morphological evidence for marine ice stream shutdown central barents sea abstract marine based ice streams are responsible for a significant proportion of the ice mass loss from the present day greenland ice sheet east antarctic ice sheet eais and west antarctic ice sheet wais but the processes controlling their initiation evolution and shutdown remain elusive hindering our understanding of how existing ice masses will respond to predicted future warming the exposed beds of palaeo ice streams offer a unique opportunity to study subglacial processes which are largely inaccessible in contemporary settings we use high resolution multibeam swath bathymetry data from the barents sea to map the geomorphology of a palaeo ice stream bed located in olgastretet olga trough approximately 75 km southeast of kong karls land and 200 km east of central svalbard this reveals evidence for shut down of a marine based ice stream followed by a phase of passive retreat or lift off of the ice stream facilitating preservation of crevasse squeeze ridges csrs subsequently active retreat of the ice margin was re established and is marked by recessional moraine ridges located upstream of the csrs previously csrs have been mainly associated with surging land terminating ice margins however our work adds to recent observations of csrs on the beds of marine based ice streams implying that they may be more common than previously thought it also indicates that marine based ice streams may switch on and off in a surge like manner which has important implications for our understanding of ice stream life cycles and the modelling of ice sheets

styles of subglacial glaciotectonic deformation within the context of the anglian ice sheet a substantial proportion of the glacial sediments of east anglia england are chaotic and highly deformed this has been attributed to a direct glaciotectonic deformation or b slumping of glaciomarine sediments we show that interpretation a leads to a classification of subglacial glaciotectonic deposits into sites of constructional deformation where little or no erosion of the preglacial deposits has occurred and styles of deformation are preserved moving up in the sequence and excavational deformation where substantial erosion of preglacial sediments has occurred and deformational styles are superimposed on each other by using glaciological and geotechnical theory we show that the expression of these deformational styles in east anglia is a natural response to the stress fields imposed by the ice sheet and that in consequence their spatial relationships are explicable the depth of deformation is related to the geotechnical properties of till and substrate the stress and effective stress fields and found to be consistent with observations

multiple late holocene surges of a high arctic tidewater glacier system in svalbard abstract most large tidewater glaciers in svalbard are known to have surged at least once in the last few hundred years however very little information exists on the frequency timing or magnitude of surges prior to the little ice age lia maximum in 1900 we investigate the sediment landform assemblages produced by multiple advances of the nathorstbreen glacier system ngs in order to reconstruct its late holocene surge history the glacier has recently undergone one of the largest surges ever observed in svalbard advancing 16 km from 2008 to 2016 we present flow velocities and ice marginal observations terminus change proglacial geomorphological processes from the later stages of this surge a first detailed assessment of the development of a glaciotectonic mud apron within the fjord during a surge is provided geomorphological and sedimentological examination of the terrestrial moraine areas formed prior to the most recent surge reveals that at least two advances were responsible for their formation based on the identification of a previously unrecognised ice contact zone recorded by the distribution of sediment facies in coastal exposures we distinguish between an outer older advance to the distal part of the moraine system and an inner younger advance to a position 2 km upfjord radiocarbon dating of shells embedded in glaciotectonic composite ridges formed by the onshore bulldozing of marine mud during the outer older of the two advances shows that it occurred at some point during the interval 700 890 cal yr bp i e 1160 ad and not during the lia as previously assumed we instead attribute the inner younger advance to the lia at 1890 by combining these data with previous marine geological investigations in inner and outer van keulenfjorden we demonstrate that ngs has advanced at least four times prior to the recent 2008 2016 surge twice at 2 7 kyr bp at 1160 ad and in 1890 this represents a unique record of the timing and magnitude of late holocene tidewater glacier surges in svalbard

new evidence for a grounded irish sea glaciation of the isles of scilly uk abstract new geomorphological and sedimentological data support previously published reconstructions of an irish sea glacier advance as far south as the northern shores of the isles of scilly in the celtic sea 49 58 n offshore boulder covered bars with cores of diamicton are interpreted as moraines which together with onshore moraine ridges and trimlines mark the maximal extent of the irish sea glacier at bread and cheese cove st martin s a heterogeneous sediment unit wedged between periglacial gelifluctates is interpreted as a mixture of glacitectonized and cannibalized glacilacustrine and marine deposits as well as primary subglacial tills macrofabric signatures reflect a subglacial origin but the whole unit has been subject to down slope mass movement micromorphological analysis indicates highly variable response to deformation and glacitectonism with most features relating to ductile behaviour and wet deformation the characteristics suggest deposition during a short lived advance of the irish sea glacier over pre existing marine and contemporaneous proglacial lacustrine sediments once blocks of stratified sediment and diamicton had been driven onshore they were subject to paraglacial remobilization resulting at most locations in complete disaggregation the distribution of re worked glacigenic sediments coincides with the glacial limits inferred from the geomorphological evidence

controlled moraine development and debris transport pathways in polythermal plateau icefields examples from tungnafellsjokull iceland a modern landsystems analogue for plateau icefield glaciation is presented based upon tungnafellsjokull in the arid cold interior of iceland landform mapping and intensive clast form analysis on three separate forelands occupied during the little ice age reveal variability in the morphology of moraines and the degree of clast modification which is interpreted as a function of the complex interplay between a the efficacy of glacial erosion b passive versus active debris transfer mechanisms and c the volume of debris provision for ice marginal freeze on mechanisms a steep outlet bounded by rockwalls produced a landform assemblage and debris transport signature typical of valley glaciers whereas two unconfined outlets produced a landform sediment imprint typical of polythermal conditions this comprises subglacial bedforms relating to the initiation of warm based ice by strain heating below icefalls at the plateau edge terminating at arcs of ice cored controlled moraine representative of frozen snout conditions patterns in clast form data on the unrestricted forelands reflect the characteristics of glacier dynamics and thermal regimes at the margin of a plateau icefield where bedrock steps of sufficient size to initiate strain heating and bedrock abrasion and plucking are located only a short distance from the marginal freeze on conditions of a snout creating debris rich folia and controlled moraine additional englacial debris may well have been carried to the glacier margin through the development of ogives and englacial thrusting at the base of the icefall thereby explaining the occurrence of striae on clasts that have otherwise been little modified by glacial abrasion copyright 2010 john wiley sons ltd

subglacial deformation at sub freezing temperatures evidence from hagafellsjokull eystri iceland abstract we report evidence of deformation at sub freezing temperatures beneath hagafellsjokull eystri an icelandic surge type glacier the bed of a piedmont lobe that advanced during the 1999 surge comprises deformed blocks of glacier ice set within frozen sediment this material has also been injected through overlying ice to form a network of crevasse squeeze ridges this layer contains evidence for two phases of deformation under contrasting rheological conditions 1 deformation under relatively warm conditions when the blocks of glacier ice acted as competent clasts within an unfrozen deforming matrix and 2 subsequent deformation at sub freezing temperatures when the ice blocks were attenuated into the surrounding frozen matrix along fractures and planar shears enriched with excess ice this suggests that the basal thermal regime of the advancing ice margin changed from warm based to cold based during the surge event the persistence and potential prevalence of subglacial sediment deformation at sub freezing temperatures has fundamental implications for our understanding of the dynamic behaviour sediment flux and geomorphic ability of cold based glaciers

discrete element modeling of subglacial sediment deformation 1 the discrete element method dem is used in this study to explore the highly nonlinear dynamics of a granular bed when exposed to stress conditions comparable to those at the bed of warm based glaciers complementary to analog experiments the numerical approach allows a detailed analysis of the material dynamics and the shear zone development during progressive shear strain the geometry of the heterogeneous stress network is visible in the form of force carrying grain bridges and adjacent volumetrically dominant inactive zones we demonstrate how the shear zone thickness and dilation depend on the level of normal overburden stress and we show how high normal stress can mobilize material to great depths the particle rotational axes tend to align with progressive shear strain with rotations both along and reverse to the shear direction the results from successive laboratory ring shear experiments on simple granular materials are compared to results from similar numerical experiments the simulated dem material and all tested laboratory materials deform by an elastoplastic rheology under the applied effective normal stress these results demonstrate that the dem is a viable alternative to continuum models for small scale analysis of sediment deformation it can be used to simulate the macromechanical behavior of simple granular sediments and it provides an opportunity to study how microstructures in subglacial sediments are formed during progressive shear strain

kuannersuit glacier revisited constraining ice dynamics landform formations and glaciomorphological changes in the early quiescent phase following the 1995 98 surge event abstract kuannersuit glacier in west greenland experienced a major surge in 1995 1998 where the glacier advanced 10 5 km down valley in this paper we examine how the quiescent phase has progressed until 2015 with respect to ice dynamics landform formations and glaciomorphological changes in the initial quiescent phase 2001 2005 ice velocities along the center flowline were 37 55 higher than ice velocities 6 3 9 0 m yr 1 in 2005 2015 and a linear relationship between ice velocity and distance from the glacier front which existed during the initial quiescent phase had disappeared in 2005 2015 between 2001 and 2015 the post surge glacier tongue thinned by 84 0 6 3 m equal to 6 0 0 5 m yr 1 the 30 m high terminal moraine detached from the active glacier along the uppermost thrust band between 2005 and 2015 after which the glacier front receded 1 5 km between the terminal moraine and the glacier front observations suggested that a proximal outwash plain was forming on top of glacier ice and that glacier naled icing aufeis was incorporated into the outwash plain in less dynamic areas with gently sloping topography along the lateral glacier margins crevasse squeeze ridges were melting out the most prominent glaciomorphological feature in 2015 was a c 1 km long gorge with c 30 40 m high ice cliffs this gorge had formed into the glacier front following the collapse of a series of chasms above the main subglacial channel roof collapse processes above subglacial channels had a significant impact on the glacier s mass loss and on the glaciomorphology during the quiescent phase earlier observations from 1913 suggest that the formation of this gorge is a reoccurring phenomenon during the quiescent phase a lower pothole field on the glacier tongue that existed during the initial quiescent phase had completely disappeared in 2015 while a larger upper pothole field in the reservoir area prevailed during the initial quiescent phase the subglacial drainage system developed into a stable channelized network although a jokulhlaup from a large ice dammed lake occurred this single event was dated to have occurred between 11 and 13 august 2006 and the lake did not refill the spatiotemporal association and evolution of glacial and glaciomorphological landforms at kuannersuit glacier are likely similar to processes at many other surging and rapidly receding glaciers of similar size

special theme modern analogues in quaternary palaeoglaciological reconstruction this issue of quaternary science reviews contains a set of five papers relating to the theme of modern analogues in quaternary palaeoglaciological reconstruction this was the subject of a special session held at the xvii inqua congress in cairns australia in 2007 at which a series of papers communicated recent advances in a the study of glacial landform sediment associations at modern glacier margins b deciphering process form relationships beneath existing ice sheets and c the use of climatic and glaciological parameters from modern glacier systems in the reconstruction of ancient ice masses each of these sub themes are aimed at improving our understanding of contemporary glacier landscape interactions and using that knowledge to make more informed palaeoglaciological reconstructions

surge of bering glacier and bagley ice field alaska an update to august 1995 and an interpretation of brittle deformation patterns in the summers of 1993 1994 and 1995 video and global positioning system location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the bering glacier and bagley ice field system alaska in an effort to characterize surge crevasse patterns and surge propagation during survey flights in late august 1995 we observed that the 1993 94 bering glacier surge was continuing and still expanding affecting new areas farther up in bagley ice field new crevasse fields similar in pattern to the first surge crevasses we had observed in june 1993 below khitrov hills and in other isolated areas of central bering glacier and in july 1994 near the head of bering glacier near the junction of bering glacier and bagley ice field in both upper bering glacier and bagley ice field were opening in eastern bagley ice field and in the steller side of bagley ice field the type of crevasses seen in the new fields suggested that the surge was propagating into these areas by analysis and interpretation of the brittle deformation patterns apparent in the crevasse patterns some aspects of the past kinematic framework of the surge can be deduced this approach may lead to a more general classification of ice surface structures and to their linkage to ongoing processes

new insights into the formation of submarine glacial landforms from high resolution autonomous underwater vehicle data abstract autonomous underwater vehicles auvs deployed close to the seafloor can acquire high resolution geophysical data about the topography and shallow stratigraphy of the seabed yet have had limited application within the fields of glacial geomorphology and ice sheet reconstruction here we present multibeam echo sounding side scan sonar sub bottom profiler and high resolution synthetic aperture sonar hisas data acquired during three auv dives on the northeast antarctic peninsula continental shelf these data enable glacial landforms including mega scale glacial lineations msgls grounding zone wedges gzws and iceberg ploughmarks to be imaged at a horizontal resolution of a few tens of centimetres allowing for the identification of subtle morphological features we map tidal ridges that are interpreted as having been formed 1 along the ice sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles and 2 by the tidally driven motion of grounded or near grounded icebergs these data also enable the mapping of small gzws that show the location of short term still stands or re advances of the ice sheet grounding zone no meltwater channels are identified from our data suggesting that free flowing meltwater may not be essential for the formation of gzws or msgls the examples presented here show how high resolution auv derived geophysical data provide a step change in our ability to image seafloor glacial landforms enabling new interpretations about past ice dynamics and glacial sedimentation at fine temporal and spatial scales

submarine glacial landforms and sedimentary environments in vaigattbogen northeastern spitsbergen abstract vaigattbogen is located in northern svalbard the area is currently affected by several tidewater glaciers this study uses multibeam sub bottom acoustic data and four sediment cores to reconstruct the late weichselian and holocene glacial history in vaigattbogen during the last glacial ice flowed northwards through vaigattbogen and fed into the hinlopen strait ice stream streamlined bedforms indicate relatively fast ice flow and their increasing elongation ratios towards the north suggest increasing flow velocities de geer moraines in the shallower parts of vaigattbogen imply that multiple halts and or re advances interrupted the ice retreat in these areas a sediment core suggests that the north basin deglaciated prior to 9 1 cal ka bp in the south basin two large moraine ridges and networks of crevasse squeeze ridges suggest that at least two surge type advances occurred during the holocene the hinlopenbreen glacier surged in the early 1970s and deposited the inner r 2 of the two large moraine ridges radiocarbon ages from a sediment core recovered from the crest of the outer r 1 ridge yield a basal age of 2 6 cal ka bp however the core did not sample subglacial diamict and the age of the ridge could be anything between 2 6 cal ka bp and early holocene the r 1 ridge formed prior to the little ice age lia implying that more than one tidewater glacier has experienced a pre lia surge on the east coast of spitsbergen suggesting that surging during the holocene was a regional phenomenon the r 1 ridge is double crested with small crevasse squeeze ridges between the crests suggesting that more than one surge type advance occurred during the holocene reaching approximately the same location data from eastern svalbard indicate differences in surge landform assemblages suggesting that different mechanisms could have governed surge cycles throughout the holocene

first geomorphological record and glacial history of an inter ice stream ridge on the west antarctic continental shelf inter ice stream areas cover significant portions of antarctica s formerly glaciated shelves but have been largely neglected in past geological studies because of overprinting by iceberg scours here we present results of the first detailed survey of an inter ice stream ridge from the west antarctic continental shelf well preserved sub and proglacial bedforms on the seafloor of the ridge in the eastern amundsen sea embayment ase provide new insights into the flow dynamics of this sector of the west antarctic ice sheet wais during the last glacial cycle multibeam swath bathymetry and parasound acoustic sub bottom profiler data acquired across a mid shelf bank between the troughs of the pine island thwaites pitpis and cosgrove palaeo ice streams copis reveal large scale ribbed moraines hill hole pairs terminal moraines and crevasse squeeze ridges together these features form an assemblage of landforms that is entirely different from that in the adjacent ice stream troughs and appears to be unique in the context of previous studies of antarctic seafloor geomorphology from this assemblage the history of ice flow and retreat from the inter ice stream ridge is reconstructed the bedforms indicate that ice flow was significantly slower on the inter ice stream ridge than in the neighbouring troughs while terminal moraines record at least two re advances or stillstands of the ice sheet during deglaciation an extensive field of crevasse squeeze ridges indicates ice stagnation subsequent to re advancing ice which deposited the field of terminal moraines in the ne the presented data suggest that the ice flow behaviour on the inter ice stream ridge was substantially different from that in the adjacent troughs however newly obtained radiocarbon ages on two sediment cores recovered from the inter ice stream ridge suggest a similar timing in the deglaciation of both areas this information closes an important gap in the understanding of past wais behaviour in the eastern ase our newly documented bedforms will also serve as an important diagnostic tool in future studies for interpreting ice sheet histories in similar inter ice stream areas

the eyjabakkajokull glacial landsystem iceland geomorphic impact of multiple surges abstract a new glacial geomorphological map of the eyjabakkajokull forefield in iceland is presented the map covers c 60 km2 and is based on high resolution aerial photographs recorded in august 2008 as well as field checking landforms are manually registered in a geographical information system arcgis based on inspection of orthorectified imagery and digital elevation models of the area we mapped subglacially streamlined landforms such as flutes and drumlins on the till plain supraglacial landforms such as ice cored moraine pitted outwash and concertina eskers and ice marginal landforms such as the large multi crested 1890 surge end moraine and smaller single crested end moraines the glaciofluvial landforms are represented by outwash plains minor outwash fans and sinuous eskers extramarginal sediments were also registered and consist mainly of old sediments in wetlands or locally weathered bedrock eyjabakkajokull has behaved as a surge type glacier for 2200 years hence the mapped landforms originate from multiple surges landforms such as large glaciotectonic end moraines hummocky moraine long flutes crevasse fill ridges and concertina eskers are characteristic for surge type glaciers the surging glacier landsystem of eyjabakkajokull serves as a modern analog to the landsystems of terrestrial paleo ice streams

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

glacial landsystems of satujokull iceland a modern analogue for glacial landsystem overprinting by mountain icecaps mapping of the surficial geology and geomorphology of the satujokull foreland of the northern hofsjokull ice cap in central iceland provides a clear signature of glacial landsystem overprinting as a result of complex glacier behaviour during the historical period landsystem 1 comprises a wide arc of ice cored moraine and controlled ridges lying outside fluted and drumlinized terrain and is indicative of polythermal conditions this landform assemblage commonly marks the historical little ice age maximum limit on the forelands of upland icefields in the arid interior of iceland and is therefore a record of climatically driven glacier advance landsystem 2 contains most of the diagnostic criteria for the surging glacier landsystem and records two separate surges by the western margin of satujokull in the period since the attainment of the little ice age maximum advance the occurrence of landsystem 2 is significant because satujokull has not been previously regarded as a surging glacier even though other outlets of hofsjokull are prone to surging landsystem overprinting especially in response to changing thermal regimes and or glacier dynamics and particularly by different flow units in the same glacier is rarely reported but is crucial to the critical application of modern landsystem analogues to quaternary palaeoglaciological reconstruction

grounding line proximal sediment characteristics at a marine based late stage ice stream margin this is the peer reviewed version of the following article ruther d c winsborrow m andreassen k forwick m 2017 grounding line proximal sediment characteristics at a marine based late stage ice stream margin journal of quaternary science 32 4 463 474 https doi org 10 1002 jqs 2939 which has been published in final form at https doi org 10 1002 jqs 2939 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

flow thermal structure and subglacial conditions of a surge type glacier temperature measurements in a subpolar surge type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas in the receiving area the glacier is cold based but bottom temperature has increased as much as 0 5 c between 1981 and 1982 and the basal heat flux is roughly 10 times the expected geothermal flux water percolation through permeable subglacial material is the probable energy source deformation of the substrate could destroy this drainage system and trigger a surge

the structural glaciology of kongsvegen svalbard and its role in landform genesis mapping of the structural glaciology of kongsvegen svalbard reveals evidence for four main deformational structures these are stratification longitudinal foliation thrusts and crevasse traces these structures are considered in terms of their contribution to debris entrainment transport and subsequent landform development stratification is associated with small amounts of supraglacial debris that has been folded with flow parallel axes longitudinal foliation in places incorporates basal glacial sediments along folds with flow parallel axes and thrusts transport basal debris to the glacier surface crevasse traces are not significant in terms of debris entrainment the entrainment of basal debris along longitudinal foliation is not a universally recognised process at kongsvegen this process is attributed to the development of a transposition foliation in combination with incorporation of debris rich basal ice or soft basal sediment in the fold complex mapping of the landforms in the proglacial area shows that debris incorporated along longitudinal foliation is released as foliation parallel ridges and that transverse ridges mark debris bearing thrusts the role of longitudinal foliation in landform development has never been documented in this manner although the preservation potential of such ridges may be limited recognition of foliation parallel ridges in the pleistocene landform record has important implications for the interpretation of the dynamics of former ire masses

concertina eskers bruarjokull iceland an indicator of surge type glacier behaviour abstract bruarjokull is a surging outlet lobe of vatnajokull in se iceland geological evidence indicates that during quiescent phases water drainage takes place in ice walled and ice roofed channels as the glacier retreats the courses of these channels are represented by eskers eskers which were englacial prior to surges become deformed during a surge the deformation of eskers reflects strong longitudinal compression of the ice in the terminal zone the wavelength of one of the compressed eskers indicates that ice in a 4 km wide margin was compressed by 50 of its original length compressed or concertina eskers date from the 1963 1964 and the 1890 surges of bruarjokull they have not been found from the 1810 surge indicating that they may not survive if overrun by subsequent surges

mud aprons in front of svalbard surge moraines evidence of subglacial deforming layers or proglacial glaciotectonics abstract large debris flow units commonly occur on the distal sides of subaqueous end moraines deposited by surges of svalbard tidewater glaciers but have rarely been described in terrestrial settings some researchers have argued that these kinds of debris flows reflect processes unique to the subaqueous environment such as the extrusion of subglacial deforming layers or extensive failure of oversteepened moraine fronts in this paper we describe terrestrial and subaqueous parts of a single late holocene moraine system deposited by a major surge of the tidewater glacier paulabreen in west spitsbergen the ice marginal landforms on land closely resemble the corresponding landforms on the seabed as evidenced by geomorphic mapping and geophysical profiles from both environments both onland and offshore extensive areas of hummocky moraine occur on the proximal side of the maximum glacier position and large mud aprons interpreted as debris flows occur on the distal side we show that the debris flow sediments were pushed in front of the advancing glacier as a continuously failing mobile push moraine we propose that the mud aprons are end members of a proglacial landforms continuum that has thrust block moraines as the opposite end member two clusters of dates 8000 ybp and 700 ybp have previously been interpreted to indicate two separate surges responsible for the moraine formation new dates suggest that the early cluster indicates a local extinction of the abounded species chlamys islandica other changes corresponding to the widespread 8 2 ka event within the fjord may suggest that the extinction of the c islandica corresponds to that time

geomorphological investigation of multiphase glacitectonic composite ridge systems in svalbard some surge type glaciers on the high arctic archipelago of svalbard have large glacitectonic composite ridge systems at their terrestrial margins these have formed by rapid glacier advance into proglacial sediments during the active surge phase creating multicrested moraine complexes such complexes can be formed during single surge advances or multiple surges to successively less extensive positions the few existing studies of composite ridge systems have relied on detailed information on internal structure and sedimentology to reconstruct their formation and links to surge processes however natural exposures of internal structure are commonly unavailable and the creation of artificial exposures is often problematic in fragile arctic environments to compensate for these issues we investigate the potential for reconstructing composite ridge system formation based on geomorphological evidence alone focusing on clear morphostratigraphic relationships between ridges within the moraine complex and relict meltwater channels outwash fans based on mapping at the margins of finsterwalderbreen in van keulenfjorden and gronfjordbreen in gronfjorden we show that relict meltwater channels that breach outer parts of the composite ridge systems are in most cases truncated upstream within the ridge complex by an inner pushed ridge or ridges at their ice proximal extents our interpretation of this relationship is that the entire composite ridge system is unlikely to have formed during the same glacier advance but is instead the product of multiple advances to successively less extensive positions whereby younger ridges are emplaced on the ice proximal side of older ridges this indicates that the finsterwalderbreen composite ridge system has been formed by multiple separate advances consistent with the cyclicity of surges being able to identify the frequency and magnitude of former surges is important as it provides insight into the past behaviour of surge type glaciers and if absolute dating is possible allows for the assessment of surge type glacier response to climate change on decadal to centennial timescales although further investigations into the internal structure of these deposits should be sought where possible our study demonstrates that geomorphology could be an invaluable tool for reconstructing the formation of composite ridge systems

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

geomorphology and sedimentology of surging glaciers a land systems approach the identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice sheet dynamics and for reconstructing ice sheets and climate no single landform or diagnostic criterion has yet been found with which to identify surging glaciers a surging glacier land system model is constructed using observations and measurements from contemporary surging glacier snouts in iceland svalbard u s a and canada for differentiating ancient surging margins from other non surging palaeoglaciers this integrates the suite of landforms sediments and stratigraphy produced at surging glacier margins landforms produced during surging include thrust moraines concertina eskers and subglacial crevasse squeeze ridges sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds which display severe glaciotectonic contortion and faulting hummocky moraine comprising interbedded stratified sediments and mass flow diamictons has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ an example of the application of the land system model is presented for east central alberta canada a surging palaeo ice stream is identified within this part of the southwestern laurentide ice sheet where thrust block moraines crevasse squeeze ridges flutings hummocky moraine and glaciotectonized sediments are juxtaposed

rapid advance of two mountain glaciers in response to mine related debris loading rapid glacier advance is known to occur by a range of mechanisms however although large scale debris loading has been proposed as a process for causing rapid terminus advance it has rarely been observed we use satellite remote sensing data to observe accelerated glacier terminus advance in response to massive supraglacial loading on two glaciers in kyrgyzstan over a 15 year period mining activity has led to the dumping of spoil of up to 180 m thick on large parts of these valley glaciers we find that the termini of these glaciers advance by 1 2 and 3 2 km respectively at a rate of up to 350 m yr 1 our analysis suggests that although enhanced basal sliding could be an important process massive supraglacial loads have also caused enhanced internal ice deformation that would account for most or all of the glacier terminus advance in addition narrowing of the glacier valley and mining and dumping of ice alter the mass balance and flow regime of the glaciers although the scale of supraglacial loading is massive this full scale experiment provides insight into glacier flow acceleration response where small valley glaciers are impacted by very large volumes of landslide debris

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

multiple origins of large hummock deposits in alai valley northern pamir implications for palaeoclimate reconstructions abstract this paper interprets the origin of several of the largest hummocky landform assemblages in the alai valley northern pamir a formerly glaciated intermontane depression the vast hummocky deposits in the koman suu and achik tash river catchments are found to be of two contrasting modes of formation glacial hummocks deposited during koman and lenin glaciers withdraw and avalanche hummocks produced during catastrophic koman and lenin rock avalanches the origins of the deposits we assessed through remote and field based geomorphological mapping as well as sedimentological investigations which included clast analysis and the identification of micro scale agglomerates indicative of rock avalanche emplacement both the koman and lenin rock avalanches were large catastrophic events with run outs of 34 and 24 km respectively and a volume over 1 109 m3 each that occurred subsequent to glacier withdrawal from the area the complex conditions on the moment of the rock avalanche emplacement promoted unusual deposits geomorphology and extensive run outs the landslide landforms formed over the pre existing glacial hummocks and fluvial deposits and are geomorphologically and sedimentologically distinct from the larger glacial hummocks the reconstruction of this sequence of events has implications for how hummock dating should be interpreted this research illustrates large scale catastrophic landsliding in the glacial environment and adds to the ongoing debate about the misidentification of rock avalanche deposits as of glacial origin and their relevance to palaeoclimatological and palaeoseismological reconstructions

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

glacier permafrost interactions processes products and glaciological implications abstract glaciers and permafrost represent key components of the global cryosphere widely held assumptions that 1 they are largely mutually exclusive and 2 glaciers resting on permafrost are slow moving and geomorphologically ineffectual have meant that glacier permafrost interactions have been given little attention within the research literature recent research however has demonstrated that such interactions are likely to have been more extensive than previously thought particularly during periods of ice sheet growth when glaciers would have advanced over pre existing permafrost work in both modern and ancient environments has revealed that subglacial processes such as basal sliding and subglacial sediment deformation can remain active at temperatures below the pressure melting point due to the persistence of premelted liquid water consequently cold based glaciers resting on permafrost are potentially more dynamic than previously thought and are capable of creating subglacial features typically viewed as only forming beneath warm based ice in addition the active coupling of cold based ice with ice marginal permafrost means such ice masses are capable of deforming sediments and occasionally bedrock to depths of tens or even hundreds of meters and are commonly associated with the development of a range of distinctive ice marginal landforms including push or thrust moraines and hummocky or controlled moraines this reflects the influence of permafrost on the entrainment of debris rich basal ice as well as the hydraulic transmissivity of the groundwater system and the associated porewater pressures within the substrate this review considers the key characteristics of permafrost and its formation likely extent and rheological behaviour within glacial environments traditional conceptions regarding the motion and landscape impact of cold based glaciers resting on permafrost are considered before their re examination in light of recent work demonstrating the operation of basal processes at sub freezing temperatures the implications for our understanding of the dynamics of glaciers and ice sheets as well as landforms and sedimentary sequences indicative of glacier permafrost interactions are explored and exemplified with reference to modern and ancient glacial environments gaps in our existing knowledge are identified and profitable areas for future research suggested

a 300 year surge history of the drangajokull ice cap northwest iceland and its maximum during the little ice age over the last 300 years each of the three surge type outlet glaciers of the drangajokull ice cap in northwest iceland has surged 2 4 times there is valuable historical information available on the surge frequencies since the little ice age lia maximum because of the proximity of the surging outlets reykjarfjar arjokull leirufjar arjokull and kaldalonsjokull to farms and pastures and monitoring of these glaciers since 1931 we have reconstructed the surge history of the drangajokull ice cap based on geomorphological mapping sedimentological studies and review of historical records geomorphological mapping of the glacier forefields reveals twice as many end moraines as previously recognized this indicates a higher surge interval than earlier perceived a clear relationship between the surge interval and climate cannot be established surges were observed more frequently during the 19th century and the earliest 20th century compared with the relatively cool 18th century and the late 20th century

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

the drumlin field and the geomorphology of the mulajokull surge type glacier central iceland article i nfo herewe presenta newgeomorphological mapof the active drumlin field and theforefieldof mulajokull a surge type outlet glacier iceland the map is based on aerial photographs taken in 1995 and lidar data recorded in 2008 mapping was done using arcgis 10 software on orthorectified imagery lidar data and digital elevation models the mapped landforms were initially identified on the aerial imagery and lidar and then ground checked in the field we mapped subglacial supraglacial ice marginal periglacial and glaciofluvial landforms the geomorphology of the mulajokull forefield is similar to that of the forefields of other surge type glaciers in iceland with a highly streamlined forefield crevasse fill ridges and series of glaciotectonic end moraines how ever thelargenumber i e 110 of drumlinsformingthe drumlin fieldisuniqueformodernicelandicsurge type glaciersand as yet unique for contemporary glaciersingeneral also apparent isthat thedrumlins are widerand shorter in the distal part of the drumlin field and narrower and longer in the proximal part hence the mapping reveals a development of the drumlins toward a more streamlined shape of the proximal landforms that have experienced more surges the drumlins in the drumlin field are active i e they form during the modern surges of mulajokull

the formation of a geometrical ridge network by the surge type glacier kongsvegen svalbard traditionally geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge crevasse fill ridges they are widely regarded as a characteristic landform of glacier surges understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record the geometrical ridge network at the surge type glacier kongsvegen in svalbard does not form by crevasse filling the networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin the transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice the thrusts were apparently formed during a glacier surge in 1948 longitudinal ridges form through the meltout of elongated pods of debris which on the glacier surface are subparallel to the ice foliation and pre date the surge this work adds to the range of landforms associated with glacier surges

ocean circulation and ice ocean interaction beneath the amery ice shelf antarctica simulations of the ocean dynamics in the cavity under the amery ice shelf antarctica were carried out using a three dimensional numerical ocean model two different boundary conditions were used to describe the open ocean barotropic exchange at the ice front the simulations show that the circulation in the ocean cavity is predominantly barotropic and is generally steered by the cavity topography the circulation is driven by the density gradient in the cavity which is strongly influenced by the heat and salt fluxes from melting and freezing processes at the ice ocean interface and by the horizontal exchange of heat and salt across the open ocean boundary at the ice front the interaction at the ice ocean interface allows the basal component of the mass loss of the amery ice shelf to be estimated in the two simulations the computed losses were 5 8 gt yr 1 and 18 0 gt yr 1 values consistent with observations the bulk of the melting occurred near the southern grounding line of the ice shelf although substantial melting also occurred in areas where heat transport by horizontal circulation was large accretion was restricted to areas where water from upstream melting became supercooled as it ascended the ice shelf base

transverse supraglacially derived crevasse infillings in a pleistocene ice sheet margin zone eastern poland genesis and sedimentary record abstract the so called crevasse infillings in the marginal zone of the saalian ice sheet in eastern poland are atypical relief forms for lowlands glaciated in the pleistocene they are located on a high of the cretaceous palaeogene substratum and form isolated ridges arranged in trains parallel to the former ice sheet margin i e transverse to the movement of the ice sheet the sedimentary succession of the crevasse infillings consists mainly of undeformed glaciodeltaic deposits we propose a model of the crevasse infilling development in three phases against the background of ice mass dynamics 1 ice sheet advance over a high of the substratum compressive ice flow that bumped against the high s slope and enrichment of the ice with debris 2 an overriding of the substratum high by ice masses a tensional ice flow regime resulted in significant crevassing and 3 ice mass stagnation low energy supraglacial deltaic sedimentation in isolated ponds between disintegrated ice blocks under frozen bed conditions considering this genesis we suggest classifying these forms as kames instead of crevasse infillings

fast flow of the lake michigan lobe evidence from sediment landform assemblages in southwestern michigan usa abstract the dynamics of the late wisconsin lake michigan lobe of the laurentide ice sheet as interpreted by sediment landform assemblages along its southeastern margin are consistent with fast flow driven by high subglacial pore pressures a major advance of the lake michigan lobe terminated at the kalamazoo moraine where proglacial glaciotectonic activity marginal stagnation and release of subglacial meltwater marked the extent of the advance a large portion of the valparaiso moraine west of the kalamazoo moraine is actually a drumlinized till capped upland plain rather than an ice marginal landform assemblage lacustrine sediment underlying the surficial diamicton in the valparaiso upland is glaciotectonically deformed to a depth of 10 m the deformed interval consists of folded sandy and silty lacustrine sediment which is in places sharply truncated by the overlying diamicton decoupling of the glacier from its bed is suggested by a discontinous thin bed of sand at the base of the diamicton and by the sharp truncation of deformed lacustrine sediment the association of drumlins proglacial and subglacial deformation marginal stagnation and major ice marginal outwash fan deposition are indicative of fast flow perhaps in a surge these characteristics are consistent with a terrestrial ice stream model for the lake michigan lobe

propagation of a glacier surge into stagnant ice the propagation of the surge of variegated glacier into its terminal lobe was observed by daily surveying of a longitudinal line of closely spaced markers extending up glacier from a stagnant zone of thin 40 m nearly motionless ice near the terminus across a front zone to a surge zone of thicker 100 m rapidly moving 20 m d 1 ice above within the front zone there were large angles of upward motion 30 compressive longitudinal strain rates 0 1 d 1 and upward vertical velocities 5 m d 1 within the surge zone the ice motion was nearly parallel to the ice surface and longitudinal gradients were small the deformation pattern produced microcracking exfoliation and buckling of surface ice longitudinal cracking longitudinal chasms and an increase in glacier volume the front zone propagated at an average speed of about 40 m d 1 or roughly twice the surge speed of the ice above the front this factor is determined by the thickness jump across the front finite element modeling constrained by measured geometry and surface velocity was used to deduce the velocity and stress at depth the velocity in the surging zone occurs almost entirely by sliding the sliding rate drops abruptly beneath the center of the front zone to zero in the stagnant zone a comparison of basal velocity and shear stress distributions indicates a highly lubricated area beneath the upper part of the front zone and a locked area beneath the lower part of the front zone normal stress at the bed is not significantly different from overburden and there is no high compressive normal stress on the bed to act as a pressure dam to obstruct water flow through the front zone

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

controlled moraines origins characteristics and palaeoglaciological implications abstract controlled moraines are supraglacial debris concentrations that become hummocky moraine upon de icing and possess clear linearity due to the inheritance of the former pattern of debris rich folia in the parent ice linearity is most striking wherever glacier ice cores still exist but it increasingly deteriorates with progressive melt out as a result moraine linearity has a low preservation potential in deglaciated terrains but hummocky moraine tracts previously interpreted as evidence of areal stagnation may instead record receding polythermal glacier margins in which debris rich ice was concentrated in frozen toe zones recent applications of modern glaciological analogues to palaeoglaciological reconstructions have implied that a controlled moraine development can be ascribed to a specific process e g englacial thrusting or supercooling and b controlled moraine preservation potential is good enough to imply the occurrence of the specific process in former glacier snouts e g ancient polythermal or supercooled snouts these assumptions are tested using case studies of controlled moraine construction in which a wide range of debris entrainment and debris rich ice thickening mechanisms are seen to produce the same geomorphic features polythermal conditions are crucial to the concentration of supraglacial debris and controlled moraines in glacier snouts via processes that are most effective at the glacier permafrost interface end moraines lie on a process form continuum constrained by basal thermal regime the morphological expression of englacial structures in controlled moraine ridges is most striking while the moraines retain ice cores but the final deposits landforms tend to consist of discontinuous transverse ridges with intervening hummocks preserving only a weak impression of the former englacial structure these are arranged in arcuate zones of hummocky moraine up to 2 km wide containing ice walled lake plains and lying down flow of streamlined landforms produced by warm based ice a variety of debris entrainment mechanisms can produce the same geomorphic signature spatial and temporal variability in process form relationships will lead to the sequential development of different types of end moraines during the recession of a glacier or ice sheet margin

unstable behavior of the laurentide ice sheet over deforming sediment and its implications for climate change geologic records of fluctuations of the laurentide ice sheet margin following the most recent glacial maximum ca 20 000 14c yr b p identify fundamental differences in ice sheet behavior depending on subglacial bed conditions rapid and irregular icemargin fluctuations occurred only over areas of deforming sediment indicating nonclimatic forcing controlled by the inherent instability of coupled ice sheet deforming sediment dynamics in contrast largely uninterrupted ice margin retreat with no evidence of significant readvance occurred over rigid bed areas indicating stable behavior unstable ice sheet behavior was most pronounced from 15 000 until 10 000 14c yr b p by which time most of the ice margin had retreated onto a rigid bed unstable ice sheet behavior would have been an integral component in controlling variable fluxes of icebergs and meltwater as well as meltwater routing to the north atlantic thus affecting thermohaline circulation the abrupt climate oscillations in the north atlantic region that ended at 10 000 14c yr b p may thus have their origin in the inherently unstable behavior of the laurentide ice sheet overriding deforming sediment

stratigraphy and sedimentology of devensian dimlington stadial glacial deposits east yorkshire england the stratigraphy and sedimentology of the glacial deposits exposed along the coast of east yorkshire are reviewed critical sections at filey brigg barmston and skipsea are examined to reassess the stratigraphy of devensian dimlington stadial glacial deposits in the light of recent developments in glacial sedimentology sedimentary and glaciotectonic structures studied in the field and by using scanning electron microscopy are emphasised two hypotheses are considered for the genesis of the interbedded diamictons and stratified sediments the first involves the deposition of lodgement till and or deformation till followed by meltout till which was overridden to produce more deformation till reflecting periods of ice stagnation punctuated by glacier thickening the second hypothesis which is favoured on the basis of field evidence and micromorphology involves the vertical accretion of a deforming till layer associated with cavity channel or tunnel valley fills beneath active ice at barmston the upper part of the diamicton contains elongate pendant structures containing gravels indicating that the diamicton was saturated and able to flow the diamictons therefore represent a complex sequence of tills deposited and deformed by active ice during the dimlington stadial previously published stratigraphical schemes involving classifications of multiple tills in east yorkshire should be simplified and it is more appropriate to assign these to a single formation the skipsea till formation rhythmic glaciolacustrine and proglacial glaciofluvial sediments overlie the tills at barmston and skipsea these were deposited in sag basins during deglaciation as the tills settled and deformed under thickening sediment and as buried ice melted out extensive sands and gravels cap the succession and were deposited on a sandur during the later stages of deglaciation

reply formation and reorientation of structure in the surge type glacier kongsvegen svalbard we welcome the development of the debate about structures at the surge type glacier kongsvegen svalbard our paper woodward et al 2002 tested a number of hypotheses proposed in the literature by glasser et al 1998 and bennett et al 1996 for sediment entrainment in glacier ice we feel that after testing sufficient evidence exists to reject these hypotheses and as a result we have proposed alternative mechanisms for the formation of these features we wish to reply to the issues raised in the above comment by glasser et al

coulomb s solution to seismic passive earth pressure on retaining walls the conventional mononobe okabe method is widely used in practice but is only applicable for calculating total seismic earth pressure of cohesionless soil not for solving earth pressure distribut

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

catastrophic landslides glacier behaviour and moraine formation a view from an active plate margin the influence of large bedrock landslides rock avalanches on the behaviour of glaciers is incompletely recognised here we present an example from an active tectonic margin in south island new zealand where large earthquakes leave a significant imprint on glacial records we demonstrate that terminal moraines on the western side of the southern alps record both ordinary i e climate driven and landslide initiated glacial advances following consideration of the processes involved in rock avalanche initiated moraine construction we suggest ways of determining the nature of the advance that built the terminal moraine the implications of these observations are important in breaking the conventional linkage of individual terminal moraines with climate forcing

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

the 1890 surge end moraine at eyjabakkajokull iceland a re assessment of a classic glaciotectonic locality abstract the glaciotectonic architecture and sequential evolution of the eyjabakkajokull 1890 surge end moraines in iceland were studied for understanding better the formation and evolution of glaciotectonic end moraines and their relation to glacier dynamics based on morphological geological and geophysical data from terrain cross profiles cross sections and ground penetrating radar profiles we demonstrate that three different qualitative and conceptual models are required to explain the genesis of the eyjabakkajokull moraines firstly a narrow single crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport secondly large lobate end moraine ridges with multiple closely spaced narrow asymmetric crests formed by proglacial piggy back thrusting thirdly a new model shows that moraine ridges with different morphologies may reflect different members of an end moraine continuum this is true for the eastern and western parts of the eyjabakkajokull moraines as they show similar morphological and structural styles which developed to different degrees the former represents an intermediate member with decollement at 4 5 m depth and 27 33 shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface the latter represents an end member with decollement at about 27 m depth and 39 horizontal shortening through multiple high amplitude overturned and overthrusted anticlines appearing as broadly spaced symmetric crests we propose that the opposite end member would be a moraine of multiple symmetric wide open anticlinal crests of low amplitude our data suggest that the glacier coupled to the foreland to initiate the end moraine formation when it had surged to within 70 190 m of its terminal position this indicates a time frame of 2 6 days for the formation of the end moraines

a reevaluation of the pallett creek earthquake chronology based on new ams radiocarbon dates san andreas fault california 1 the pallett creek paleoseismic record occupies a keystone position in most attempts to develop rupture histories for the southern san andreas fault previous estimates of earthquake ages at pallett creek were determined by decay counting radiocarbon methods that method requires large samples which can lead to unaccounted sources of uncertainty in radiocarbon ages because of the heterogeneous composition of organic layers in contrast accelerator mass spectrometry ams radiocarbon dates may be obtained from small samples that have known carbon sources and also allow for a more complete sampling of the section we present 65 new ams radiocarbon dates that span nine ground rupturing earthquakes at pallett creek overall the ams dates are similar to and reveal no dramatic bias in the conventional dates for many layers however individual charcoal samples were younger than the conventional dates leading to earthquake ages that are overall slightly younger than previously reported new earthquake ages are determined by bayesian refinement of the layer ages based on stratigraphic ordering and sedimentological constraints the new chronology is more regular than previously published records in large part due to new samples constraining the age of event r the closed interval from event c to 1857 has a mean recurrence of 135 years 83 2 years and a quasiperiodic coefficient of variation cov of 0 61 we show that the new dates and resultant earthquake chronology have a stronger effect on cov than the specific membership of this long series and dating precision improvements from sedimentation rates

using uav acquired photography and structure from motion techniques for studying glacier landforms application to the glacial flutes at isfallsglaciaren 2016 the authors earth surface processes and landforms published by john wiley sons ltd glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small scale fragile geomorphological features which could provide insight into subglacial or submarginal processes subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor relief landforms as wind weather water and vegetation impact on the newly exposed surface ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes here we used an unmanned aerial vehicle to capture close range aerial photography of the foreland of isfallsglaciaren a small polythermal glacier situated in swedish lapland an orthophoto and a digital elevation model with 2 cm horizontal resolution were created from this photography using structure from motion software these geospatial data was used to create a geomorphological map of the foreland documenting moraines fans channels and flutes the unprecedented resolution of the data enabled us to derive morphological metrics length width and relief of the smallest flutes which is not possible with other data products normally used for glacial landform metrics mapping the map and flute metrics compare well with previous studies highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution the vast majority of flutes were found to have an associated stoss side boulder with the remainder having a likely explanation for boulder absence burial or erosion furthermore the size of this boulder was found to strongly correlate with the width and relief of the lee side flute this is consistent with the lee side cavity infill model of flute formation whether this model is applicable to all flutes or multiple mechanisms are required awaits further study 2016 the authors earth surface processes and landforms published by john wiley sons ltd

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

sedimentation and stratigraphy at eyjabakkajokull an icelandic surging glacier a model for sedimentation by surging glaciers is developed from analysis of the debris load sedimentary processes and proglacial stratigraphy observed at the icelandic surging glacier eyjabakkajokull three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce a sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures failure and glacitectonic deformation of the overridden sediments b reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses these induce intense folding and thrusting during which basal debris rich ice is elevated into an englacial position in a narrow marginal zone as the terminal area of the glacier stagnates between surges debris from this ice is released supraglacially and deposited by meltout and sediment flows c local variations in overburden pressure beneath stagnant crevassed ice cause subglacial lodgement tills which are sheared during surges to flow into open crevasses and form crevasse fill ridges

large scale reorganization and sedimentation of terrestrial ice streams during late wisconsinan laurentide ice sheet deglaciation glacial geomorphological mapping of shuttle radar topography mission srtm data from the western canadian prairies demonstrates that during the last late wisconsinan deglaciation of the laurentide ice sheet terrestrial ice streams underwent a major reorganization of their flow configuration this reorganization involved a 90 shift in flow direction and was accompanied by a corresponding increase in the influence of topography on streaming flow ice streams included both topographically confined and pure ice streams that flowed independent of topography streaming flow is recorded by suites of highly elongate 60 km long subglacial bedforms bounded sharply at their lateral margins by prominent moraines initial streaming flow was unconfined by topography but was replaced progressively and crosscut by younger topographically confined flows flow reorganization is inferred to have been caused by temporal and spatial variations in the interaction between frozen and thawed bed conditions with thinning and shutdown of one ice stream ultimately triggering initiation of others this highlights the role of internal glaciodynamically driven reorganization in triggering streaming flow within large ice sheets and shows that large scale flow reorganization can occur over the time scale of a single deglaciation in terrestrial ice streams

the tekapo glacier new zealand during the last glacial maximum an active temperate glacier influenced by intermittent surge activity abstract quaternary glaciations have created impressive landform assemblages that can be used to understand palaeo glacier extent character and behaviour and hence past global and local glacier forcings however in the southern hemisphere and especially in new zealand the quaternary glacial landform record is relatively poorly investigated with regard to glaciological properties in this study a 1 m digital elevation model dem was generated from airborne lidar data and supplemented with aerial imagery and field observations to analyse the exceptionally well preserved glacial geomorphology surrounding lake tekapo new zealand we describe a rich suite of last glacial maximum lgm and recessional ice marginal subglacial supraglacial glaciofluvial and glaciolacustrine landform assemblages these represent two landsystems comprising i fluted till surfaces with low relief push moraine ridges and ii crevasse squeeze ridges zig zag eskers and attenuated lineations the former landsystem records the behaviour of an active temperate glacier and the latter landsystem which is superimposed upon and inset within the former strongly suggests intermittent surge phases the two landsystem signatures indicate a sequential change in ice marginal dynamics during recession that was likely to have been partially non climatically driven overall we present the first evidence of surge type glacier behaviour in new zealand

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment

till and moraine emplacement in a deforming bed surge an example from a marine environment the glacier sefstrombreen in spitsbergen surged across an arm of the sea between qsr 1882 and 1886 and rode up onto the island coraholmen marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location transported and smeared over the sea bed and coraholmen as a deformation till the glacier emplaced about 210sm 0 2 km 3 of drift in the terminal 2 km of its advance in a maximum of 14 years leaving a thickness of up to 20 m on coraholmen which was doubled in size as a result during the surge subglacial muds were characterised by high water pressures low effective pressures and low frictional resistance to glacier movement original sedimentary inhomogenities permit fold structures to be identified but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills the surge was probably shortlived and as the heavily crevassed glacier stagnated underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface reticulate crevasse intrusion ridges on coraholmen and the sea floor reflect the orientation of surge generated crevasses water and sediment was also extruded beyond the glacier at its maximum extent to form extensive flows producing till tongues both on coraholmen and the sea floor extending over 1 3 km from the glacier it is argued that subglacial deformation of pre existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre existing sediments but will also play a fundamental role in glacier dynamics criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed copyright 1996 elsevier science ltd