subglacial bed form morphology controlled by ice speed and sediment thickness subglacial bed forms drumlins ribbed moraines and megascale glacial lineations are enigmatic repetitive flow parallel and flow transverse landforms common in glaciated landscapes their evolution and morphology are a potentially powerful constraint for ice sheet modeling but there is little consensus on bed form dynamics or formative mechanisms here we explore shallow sediment bed form dynamics via a simple model that iterates i down flow till flux ii pressure gradient driven till flux and iii entrainment and deposition of sediment under various boundary conditions replicas of subglacial bed forms readily emerge bed form dynamics mirror those in subaqueous and aeolian domains transitions between ribbed moraines and elongate flow parallel bed forms are associated with increasing ice speeds and declining sediment thickness these simulations provide quantitative flux estimates and suggest that widely observed transitions in shallow sediment subglacial bed forms e g ribbed moraines to drumlinoids to megascale glacial lineations are manifestations of subtle variations in ice velocity and sediment thickness

the instability theory of drumlin formation and its explanation of their varied composition and internal structure despite their importance in understanding glaciological processes and constraining large scale flow patterns in palaeo glaciology there is little consensus as to how drumlins are formed attempts to solve the drumlin problem often fail to address how they are created from an initially flat surface in the absence of obvious cores or obstacles this is a key strength of the instability theory which has been described in a suite of physically based mathematical models and proposes that the coupled flow of ice and till causes spontaneous formation of relief in the till surface encouragingly model predictions of bedform height and length are consistent with observations and furthermore the theory has been applied to a range of subglacial bedforms and not just drumlins however it has yet to confront the myriad observations relating to the composition and internal structure of drumlins and this could be seen as a major deficiency this paper is a first attempt to assess whether the instability theory is compatible with the incredible diversity of sediments and structures found within drumlins we summarise the underlying principles of the theory and then describe and attempt to explain the main types of drumlin composition e g bedrock till glaciofluvial sediments and combinations thereof contrary to a view which suggests that the presence of some sedimentary sequences e g horizontally stratified cores is inconsistent with the theory we suggest that one would actually expect a diverse range of constituents depending on the inheritance of sediments that pre date drumlin formation the duration and variability of ice flow and the balance between erosion and deposition till continuity at the ice bed interface we conclude that the instability theory is compatible with and potentially strengthened by what is known about drumlin composition and as such offers the most complete and promising solution to the drumlin problem to date

how do bedform patterns arise new views on the role of bedform interactions within a set of boundary conditions one explanation for bedform patterns is self organization in which the pattern emerges because of interactions among the bedforms themselves models remote images field studies and lab experiments have identified bedform interactions that involve whole bedforms only bedform defects or that are remote interactions between bedforms it is proposed that bedform interactions form a spectrum from constructive to regenerative in pattern development constructive interactions including merging lateral linking cannibalization and remote transfer of sediment push the system toward fewer larger more widely spaced bedforms regenerative interactions including bedform splitting defect creation and calving push the system back toward a more initial state other interactions including off center collision defect migration and bedform and defect repulsion cause pattern change but may not be strongly constructive or regenerative although bedform interactions are ubiquitous to any field of bedforms their dynamics flow field modification and impact upon measurable pattern parameters are yet poorly understood most bedform interactions span bedform types and fluids supporting the hypothesis that pattern emerges from dynamics at the bedform level in a hierarchy that includes lower levels of bedform flow and grain fluid interactions bedform interactions alone however cannot account for the rich diversity of bedform patterns in nature it is proposed that field diversity arises because of boundary conditions which are the environmental variables within which a field evolves conceptually boundary conditions modify the shape of the attractor toward which a field evolves possibly by altering the type and frequency of bedform interactions boundary conditions are broadly similar within system types but are unique for each bedform field so that no two are ever exactly alike although aeolian and fluvial systems share some types of boundary conditions flow depth is a unique boundary condition in shallow fluvial systems copyright 2009 john wiley sons ltd

size and shape characteristics of drumlins derived from a large sample and associated scaling laws abstract ice sheets flowing across a sedimentary bed usually produce a landscape of blister like landforms streamlined in the direction of the ice flow and with each bump of the order of 102 to 103 m in length and 101 m in relief such landforms known as drumlins have mystified investigators for over a hundred years a satisfactory explanation for their formation and thus an appreciation of their glaciological significance has remained elusive a recent advance has been in numerical modelling of the land forming process in anticipation of future modelling endeavours this paper is motivated by the requirement for robust data on drumlin size and shape for model testing from a systematic programme of drumlin mapping from digital elevation models and satellite images of britain and ireland we used a geographic information system to compile a range of statistics on length l width w and elongation ratio e where e l w for a large sample mean l is found to be 629 m n 58 983 mean w is 209 m and mean e is 2 9 n 37 043 most drumlins are between 250 and 1000 metres in length between 120 and 300 metres in width and between 1 7 and 4 1 times as long as they are wide analysis of such data and plots of drumlin width against length reveals some new insights all frequency distributions are unimodal from which we infer that the geomorphological label of drumlin is fair in that this is a true single population of landforms rather than an amalgam of different landform types drumlin size shows a clear minimum bound of around 100 m horizontal maybe drumlins are generated at many scales and this is the minimum or this value may be an indication of the fundamental scale of bump generation proto drumlins prior to them growing and elongating a relationship between drumlin width and length is found with r2 0 48 and that is approximately w 7 l 1 2 when measured in metres a surprising and sharply defined line bounds the data cloud plotted in e w l space and records a scale dependent maximum elongation limit approximated by emax l1 3 when l measured in metres for a given length for some reason as yet unknown drumlins do not exceed the elongation ratio defined by this scaling law we also report and compare our statistics to an amalgamated sample 25 907 drumlins of measures derived from around 50 published investigations any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling

potential sea level rise from antarctic ice sheet instability constrained by observations large parts of the antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine ice sheet instability misi a self sustaining retreat of the grounding line triggered by oceanic or atmospheric changes there is growing evidence that misi may be underway throughout the amundsen sea embayment ase which contains ice equivalent to more than a metre of global sea level rise if triggered in other regions the centennial to millennial contribution could be several metres physically plausible projections are challenging numerical models with sufficient spatial resolution to simulate grounding line processes have been too computationally expensive to generate large ensembles for uncertainty assessment and lower resolution model projections rely on parameterizations that are only loosely constrained by present day changes here we project that the antarctic ice sheet will contribute up to 30 cm sea level equivalent by 2100 and 72 cm by 2200 95 quantiles where the ase dominates our process based statistical approach gives skewed and complex probability distributions single mode 10 cm at 2100 two modes 49 cm and 6 cm at 2200 the dependence of sliding on basal friction is a key unknown nonlinear relationships favour higher contributions results are conditional on assessments of misi risk on the basis of projected triggers under the climate scenario a1b ref 9 although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss we find that contributions are restricted by a combination of these constraints calibration with success in simulating observed ase losses and low assessed risk in some basins our assessment suggests that upper bound estimates from low resolution models and physical arguments up to a metre by 2100 and around one and a half by 2200 are implausible under current understanding of physical mechanisms and potential triggers

the morphological characteristics of ribbed moraine abstract ribbed rogen moraines are large subglacially formed transverse ridges that cover extensive areas of the former laurentide scandinavian and irish ice sheets given their ubiquitous and conspicuous nature it is surprising that their characteristics are poorly understood to date most ribbed moraine studies have been spatially restricted and rely on small sample sizes thus published accounts of their characteristics are most likely unrepresentative of ribbed moraines generally this study addresses this deficit by producing the first representative data set on ribbed moraine size shape pattern and distribution and we describe their spatial characteristics various remote sensing and gis techniques were used to map ribbed moraines over a combined area of 81 000 km 2 in canada ireland and sweden producing a database of just over 33 000 individual landforms in all 25 082 ridges were mapped in two areas in central and northern quebec the lac naococane and river kaniapiskau regions 5637 in the lake rogen area of central sweden and 2500 in north central ireland in comparison against the published accounts of ribbed moraine we demonstrate that some widely held assertions are inaccurate or untrue and we show that ribbed moraine morphological characteristics are more complex than has been hitherto reported our data reveals they exist over a larger scale range than was previously stated this study concludes by presenting a list of ribbed moraine characteristics and argues that formational hypotheses must account for these if they are to remain valid explanations of ribbed moraine genesis

relationship between mega scale glacial lineations and iceberg ploughmarks on the bjornoyrenna palaeo ice stream bed barents sea abstract mega scale glacial lineations msgls are ridge groove corrugations aligned in the direction of the former ice flow tens of kilometers long and up to a few hundred meters wide they are the most striking subglacial features on the beds of former ice streams and play an important role in modulating ice flow through their influence on bed roughness and subglacial hydrology despite the importance of msgls their formation remains enigmatic most studies have tended to focus on assemblages of msgls and their relationship to other landforms up ice e g drumlins or bedrock features in ice stream onset zones but fewer studies have examined their characteristics and transition to other landforms towards ice stream grounding lines in this paper we investigate the relationship between an assemblage of msgls and ploughmarks on the bed of the former bjornoyrenna ice stream in the sw barents sea which occurs in the central part of the ice stream bed a sample of msgls is used to test their potential origin based on their metrics width length and diagnostic characteristics predicted by formation theories results show a down flow depth decrease of the msgl grooves and a shallowing tendency once they transition into ploughmarks their width shows an increasing tendency which we link mostly to the strong divergence of the trough and ice flow downstream the prominent continuity from linear to curvilinear features demonstrates that the grooves associated with msgls transition into iceberg ploughmarks this observation is consistent with the hypothesis that the msgls have formed through a mechanism of groove ploughing at least in part the continuity from msgls to iceberg ploughmarks resulted from detachment of large icebergs from the grounded ice wall or grounded ice shelf and their ploughing away from the ice margin

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

a theory for ice till interactions and sediment entrainment beneath glaciers and frozen onto or melted from the glacier base can achieve a steady state that is in balance with the rate that latent heat is transported to or from the basal interface at constant n when a gradual increase in heat flow from the glacier base causes the rate of melting to decrease h increases and continues to do so when the heat flow is great enough to produce freezing as freezing becomes more rapid and h increases further the rate of fluid supply to the glacier base reaches a maximum when the effective permeability is sufficiently reduced by the partial ice saturation in the fringe larger h can be achieved with slower freezing at the glacier base but steady states with larger h are unstable the maximum rate of fluid supply to the glacier base is greater at lower n higher temperature gradients and for sediments with higher permeabilities unsteady behavior can lead to large changes in h when there is a mismatch between the rate that latent heat can be extracted and the rate that fluid is supplied to the glacier base transient behavior driven by abrupt changes in n is characterized by rapid variations in freezing rate followed by slower adjustments to h that are limited by the timescale for the conduction of latent heat the resulting patterns of sediment deformation are expected to commonly be distributed over finite depth ranges even when shear is perfectly localized at any single instant in time

the periodic topography of ice stream beds insights from the fourier spectra of mega scale glacial lineations ice stream bed topography contains key evidence for the ways ice streams interact with and are potentially controlled by their beds here we present the first application of two dimensional fourier analysis to 22 marine and terrestrial topographies from 5 regions in antarctica and canada with and without mega scale glacial lineations msgls we find that the topography of msgl rich ice stream sedimentary beds is characterized by multiple periodic wavelengths between 300 and 1200 m and amplitudes from decimeters to a few meters this periodic topography is consistent with the idea that instability is a key element to the formation of msgl bedforms dominant wavelengths vary among locations and on one paleo ice stream bed increase along the direction of ice flow by 1 7 0 52 km 1 we suggest that these changes are likely to reflect pattern evolution via downstream wavelength coarsening even under potentially steady ice stream geometry and flow conditions the amplitude of msgls is smaller than that of other fluvial and glacial topographies but within the same order of magnitude however msgls are a striking component of ice stream beds because the topographic amplitude of features not aligned with ice flow is reduced by an order of magnitude relative to those oriented with the flow direction this study represents the first attempt to automatically derive the spectral signatures of msgls it highlights the plausibility of identifying these landform assemblages using automated techniques and provides a benchmark for numerical models of ice stream flow and subglacial landscape evolution

spatial organisation of drumlins ice sheets flowing over soft sediments produce undulations in the bed typically of metres in relief of which drumlins are the most abundant and widely investigated consensus regarding their mechanism of formation has yet to be achieved in this paper we examine the spatial organisation of drumlins in order to provide an improved description of the phenomenon and to guide hypotheses of their formation we review the literature highlighting contradictory findings regarding drumlin spatial organisation and then use this to motivate our study based on a large sample 42 488 of drumlins from canada britain and norway are there typical arrangements in drumlin positioning and are they organised in a regular spatial manner patterned or are they distributed randomly we recognise that drumlin fields are inherently patchy and therefore apply inhomogeneous spatial statistics in order to study their distribution this shows that whilst drumlins are occasionally randomly placed their main state is non random they exhibit a strong and statistically significant signal of regularity across lengths scales of 100 1200 m we conclude that patterning is a near ubiquitous property of drumlins this finding of regularity demonstrates spatial self organisation in the bedforming process with drumlins as an emergent manifestation of subglacial sediment mobility kilometre scale interactions between drumlins must occur as they evolve or interactions may arise as a consequence of growth or migration hypotheses or models are required that can explain the regular spacing of drumlins we highlight three suggestions for such self organisation instability in the coupling of ice flow sediment flux bed shape local feedback between sediment mobility and relief and coarsening by growth or migration

pressure dependent viscosity and interfacial instability in coupled ice sediment flow we study an interfacial instability in the coupled flow of ice and subglacial sediment both modelled as viscous media unlike other interfacial instabilities in coupled viscous flows at zero reynolds number the mechanism considered here does not rely on buoyancy or the effect of an upper free surface but on the pressure dependence of the sediment viscosity specifically the instability relies on sediment rheology being such that when sediment flows in simple shear sediment flux increases with compressive normal stress at the ice sediment interface when the velocity of the interface is kept constant when ice moves over a shallow bump in the interface it generates a higher compressive stress on the bump s upstream side than in its lee if in addition the effective sediment viscosity is low compared with that of ice interfacial velocity remains approximately constant and this then implies that more sediment flows into the bump than out of it causing it to grow modelling ice as a newtonian material we show that this mechanism works for a wide range of sediment rheologies including the highly nonlinear shear thinning ones typically thought most appropriate for the description of nearly plastic sediment the instabilities predicted are essentially two dimensional with infinite transverse wavelength and a nonlinear model shows that growth is unbounded until cavitation occurs in the lee of evolving bumps on the interface the instability mechanism does not seem to predict the formation of common glacial landforms but may explain the formation of water filled cavities on deformable glacier beds

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

ribbed moraines in northern manitoba canada characteristics and preservation as part of a subglacial bed mosaic near the core regions of ice sheets abstract ribbed moraines are enigmatic glacial landforms for which different models with contrasting paleoglaciologic implications have been proposed to explain their formation despite the great deal of attention this type of landform has received over the last several decades ribbed moraine fields in northern manitoba canada are among the largest in the world but have been seldom studied ribbed moraines in this part of the world overlie the low relief canadian shield are not constrained by topography and are part of a spatial subglacial landform assemblage associated with drumlinoid ridges within palimpsest and relict type glacial terrain zones field observations herein provide new insights into the characteristics of these transverse to ice flow ridges at landscape mapping and spatial analysis and landform internal structure using high resolution shear wave s wave seismic reflection surveys sedimentological characteristics clast fabric analyses scales two main types of ribbed moraine are recognized pristine high amplitude straight crested ridges and secondarily modified subdued drumlinized ridges ribbed moraine in northeast manitoba consist of massive matrix supported till at surface which is similar in matrix texture and composition to the regional till sheet though pristine moraines show a higher concentration of boulders a seismic profile reveals subparallel to surface layered stratigraphy with only minor folding and no major unconformities stacking or faulting the demonstrated fragmentary nature of ribbed moraine fields the inherited signature of the till within these fields the secondary patchy drumlinization of the ridges and the more abundant granitoid outcrops in areas of intense modification all suggest that subglacial ribbed moraine formed from pre existing sediments and were later preserved and or partially reworked through a regional mosaic of shifting subglacial bed conditions we therefore make the case that pristine unmodified moraines were preserved beneath stable sticky spots we support a link between ribbed moraine and widespread cold based and or dewatered subglacial conditions in inner core regions of ice sheets but for reasons of preservation and not necessarily formation

evolution of lumpy glacial landscapes at 10 100 m scales glaciated landscapes are lumpy sporting rocky bedforms with abraded upvalley faces and sharp quarried downvalley edges using models that operate at two time scales i address glacial landform development at these scales in order to explore the dependence of bed topography and erosion rate on glacier and rock properties sliding at the bed a prerequisite for both abrasion and quarrying is strongly modulated by water pressures short time scale models designed to capture the transient hydro sliding system beneath a temperate glacier quantify the temporal and spatial pattern of effective stress on the glacier bed the bed is subjected to repetitive stressing focused on the edges of bed steps the frequency and magnitude of stress events increasing with ice thickness the numerical model of bed evolution at longer time scales incorporates both abrasion and quarrying of fracture bound blocks the probability of quarrying of a block by a particular stress event is taken to depend inversely upon both block size and the depth of the niche in which it sits upglacier migrating rock bedforms with 10 100 m wavelengths inevitably emerge reflecting efficient quarrying of blocks from downvalley facing steps in the bed the relative importance of abrasion and quarrying and bed roughness are controlled by fracture spacing and major steps in the valley floor are attributable to transitions in fracture spacing

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

morphometry and core type of streamlined bedforms in southern sweden from high resolution lidar abstract this paper generates a new data set of streamlined glacial bedforms in southern sweden which is used both to test conclusions from previous work on streamlined bedform morphometrics and to advance our knowledge of streamlined bedforms on the scandinavian shield the data set consists of streamlined glacial bedforms in southeast sweden mapped from the new lidar derived swedish national height model which has a pixel resolution of 2 0 m with a vertical resolution of 1 cm we have mapped 10 311 features of the mapped features 135 are known to have an unconsolidated sediment core 2120 a bedrock component and 8055 whose core composition is unknown the extracted morphological variables are then subjected to a univariate and bivariate analysis we find that the extracted characteristics broadly fit into the lower end of the modal and median value spectrum of similar bedforms from around the world the distribution of the variables is found to be log normal to a first order approximation the covariant relationships between height and length width and area are examined after the variables have been log transformed and are found to be significant if not particularly strong rock cored features are found to have a longer modal length than soft cored features which suggests that reconstructions of past flow velocities from streamlined landforms need to closely consider core type additionally we find no support for a derived scaling law for streamlined features by plotting length width and elongation ratio against one another

geomorphology under ice streams moving from form to process ice streams are integral components of an ice sheet s mass balance and directly impact on sea level their flow is governed by processes at the ice bed interface which create landforms that in turn modulate ice stream dynamics through their influence on bed topography and basal shear stresses thus ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics this paper reviews developments in our understanding of ice stream geomorphology from an historical perspective with a focus on the extent to which studies of modern and palaeo ice streams have converged to take us from a position of near complete ignorance to a detailed understanding of their bed morphology during the 1970s and 1980s our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in antarctica very few palaeo ice streams had been identified with any confidence during the 1990s however glacial geomorphologists began to recognise their distinctive geomorphology which included distinct patterns of highly elongated mega scale glacial lineations ice stream shear margin moraines and major sedimentary depocentres however studying relict features could say little about the time scales over which this geomorphology evolved and under what glaciological conditions this began to be addressed in the early 2000s through continued efforts to scrutinise modern ice stream beds at higher resolution but our current understanding of how landforms relate to processes remains subject to large uncertainties particularly in relation to the mechanisms and time scales of sediment erosion transport and deposition and how these lead to the growth and decay of subglacial bedforms this represents the next key challenge and will require even closer cooperation between glaciology glacial geomorphology sedimentology and numerical modelling together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams

active drumlin field revealed at the margin of mulajokull iceland a surge type glacier abstract recent marginal retreat of mulajokull a surge type outlet glacier of hofsjokull iceland has revealed a drumlin fi eld consisting of more than 50 drumlins the drumlins are 90 320 m long 30 105 m wide 5 10 m in relief and composed of multiple beds of till deposited by lodgment and bed deformation the youngest till layer truncates the older units with an erosion surface that parallels the drumlin form thus the drumlins are built up and formed by a combination of subglacial depositional and erosional processes field evidence suggests each till bed to be associated with individual recent surges we consider the fi eld to be active in the sense that the drumlins are shaped by the current glacial regime the mulajokull fi eld is the only known active drumlin fi eld and is therefore a unique analogue to pleistocene drumlin fi elds

a case study in the new york drumlin field an investigation using microsedimentology resulting in the refinement of a theory of drumlin formation abstract the formation of drumlins remains a major enigma it is accepted that drumlins form under active temperate ice most likely within a soft sediment deforming bed at ephemeral sticky points these sticky points likely lead to the causative mechanism around which sediment nucleation occurs the critical question is under what conditions and where and how do sticky spots form a comparative investigation of a drumlin and mega flute in the new york drumlin field as a case study demonstrates that rheological and sedimentological tills from these different forms are similar it is not therefore rheological change alone that must account for drumlin shape and form but likely the advective subglacial basal sediment flux rate at the ice bed the rate of sediment motion between the upper interface at the ice sediment bed boundary and the lower immobile sediment at depth is crucial at the lower decollement between the mobile and immobile sediment units within the deforming sediment package proto drumlin nucleation is likely to occur and develop into a streamlined form the trigger mechanism for such a perturbation is a derivative of sediment rheology and sediment flux rate driven by the overlying ice stresses recent evidence from antarctica lends credence to this new hypothesis that can be related to all drumlins formed under temperate soft sediment deforming bed conditions

glacial geomorphological mapping a review of approaches and frameworks for best practice geomorphological mapping is a well established method for examining earth surface processes and landscape evolution in a range of environmental contexts in glacial research it provides crucial data for a wide range of process oriented studies and palaeoglaciological reconstructions in the latter case providing an essential geomorphological framework for establishing glacial chronologies in recent decades there have been significant developments in remote sensing and geographical information systems gis with a plethora of high quality remotely sensed datasets now often freely available most recently the emergence of unmanned aerial vehicle uav technology has allowed sub decimetre scale aerial images and digital elevation models dems to be obtained traditional field mapping methods still have an important role in glacial geomorphology particularly in cirque glacier valley glacier and icefield ice cap outlet settings field mapping is also used in ice sheet settings but often takes the form of necessarily highly selective ground truthing of remote mapping given the increasing abundance of datasets and methods available for mapping effective approaches are necessary to enable assimilation of data and ensure robustness this paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available with a focus on their applicability in particular glacial settings we distinguish two overarching work streams that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes i mapping of ice sheet geomorphological imprints using a combined remote sensing approach with some field checking where feasible and ii mapping of alpine and plateau style ice mass cirque glacier valley glacier icefield and ice cap geomorphological imprints using remote sensing and considerable field mapping key challenges to accurate and robust geomorphological mapping are highlighted often necessitating compromises and pragmatic solutions the importance of combining multiple datasets and or mapping approaches is emphasised akin to multi proxy approaches used in many earth science disciplines based on our review we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment comparison and integration of geomorphological data these will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions finally we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and or sedimentological evidence and that such data should ideally be collected as part of a holistic assessment of the overall glacier system

real barchan dune collisions and ejections 1 from high resolution satellite imagery of barchan sand dunes we provide geomorphological evidence of collisions that result in the ejection of a barchan from the wake of another barchan dune previous interpretations suggest this outcome is evidence of soliton or solitary wave behaviour however the physical mechanisms for mass exchange are not fully understood resulting in debate our evidence and interpretation indicates that mass is transferred to the upwind barchan by shadowing a portion of downwind barchan s stoss slope turbulent unsaturated airflow erodes the surface between the dunes creating a smaller dune that ejects from the wake region previous observations lacked the spatial resolution required to document this process therefore our observations clarify the collision dynamics of barchans a broader implication of our observations is the role of collisions in maintaining an equilibrium size distribution in barchan swarms

grain boundary microstructures in micaceous quartzite significance for fluid movement and deformation processes in low metamorphic grade shear zones observation by scanning electron microscopy of a sericitic quartzite from a low grade 1 cm wide shear band developed from an originally pure quartzite revealed a nonconnected intergranular porosity the isolated pores occur principally on quartz quartz grain boundaries pores surrounding isolated mica flakes show very irregular geometries reflecting a highly unstable disequilibrium crystal fluid interface but regular frequently crystallographic pore shapes predominate in other grain boundaries statistical analysis reveals that the pores are principally concentrated on grain boundaries oriented perpendicular to the two foliations developed within the shear band i e grain boundaries at 45 and 90 to the shear band boundaries indicating that the fluid phase occupied extensional sites relative to both the overall and local scale of one microlithon strain ellipsoids there is a strong spatial relationship between interfacial porosity and the presence of mica with the most porous grains occurrin

physical environment of drumlin formation review of published descriptions of drumlin fields suggests that the following conditions are important to drumlin growth 1 compressive longitudinal and possibly extending transverse strain rates in the ice 2 thin ice such as occurs near the glacier margin and 3 high pore water pressure in the subglacial sediments most drumlin fields display all of these and no fields of well developed drumlins were found that did not on the oilier hand the lithology of drumlin forming sediment appears not to be important in promoting drumlin growth since it varied widely nor are the lithology and large scale topography of the bed

do subglacial bedforms comprise a size and shape continuum understanding the evolution of the ice bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created however the formation of the suite of landforms generated at this boundary subglacial bedforms is a contentious issue that is yet to be fully resolved bedforms formed in aeolian fluvial and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes for subglacial bedforms a size and shape continuum has been hypothesised yet it has not been fully tested here we analyse the largest data set of subglacial bedform size and shape measurements ever collated 96 900 bedforms our results show that flutes form a distinct population of narrow bedforms however no clear distinction was found between drumlins and megascale glacial lineations msgls which form a continuum of subglacial lineations a continuum of subglacial ribs also exists with no clear size or shape distinctions indicating separate populations furthermore an underreported class of bedform with no clear orientation to ice flow quasi circular bedforms overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two potentially merging these three bedform types into a larger continuum

electromagnetic resistivity anisotropy in till from the kiskatinaw streamlined landform field northeastern british columbia canada abstract applications of the azimuthal electromagnetic em method that establish the internal structure of landforms consisting of sediment are sparse in the kiskatinaw streamlined landform field of northeastern british columbia ice flow parallel till ridges formed beneath the cordilleran ice sheet during the late wisconsinan em anisotropy data from the kiskatinaw field are systematically related to ridge elongation and orientation and in part to clast fabrics however in contrast to previous studies we find that resistivity measurements do not necessarily record the orientation of ice flow and electrical anisotropy in till may not be a simple indicator of ice flow direction for highly elongate ridges l w 3 the long axes of resistivity ellipses are at high angles to the long axes of the landforms tills in these elongate ridges are matrix rich 85 and display strong unimodal ice flow parallel clast fabrics for more equant ridges l w

drumlin sedimentology in a hard bed lowland setting connemara western ireland implications for subglacial bedform generation in areas of sparse till cover cores of coastal drumlins in connemara contain stratified diamictons that interdigitate with gravelly clinoforms and finer grained rhythmites the diamictons are interpreted as subaqueous mud apron deposits delivered by subglacial till advection to continuously failing subaqueous ice contact fans whose strata were being syn depositionally over steepened by glacitectonic deformation the localized nature of the stratified sediments reflects the emergence of subglacial deforming tills and meltwater deposits in a glacilacustrine environment to produce interdigitated mass flow diamictons and grounding line fans wedges these depo centres became glacitectonized and subglacially streamlined during glacier overriding and hence regional drumlin sedimentology reflects the varying degrees of inheritance of pre existing glacigenic deposits and suggests that drumlin production relates more to the position of localized sediment accumulations at the glacier bed than full depth till deformation processes e g instability mechanisms within the same drumlin field till cored drumlins give way down ice to stratified cored drumlins with till caps and then to stratified drumlins this zonation is compatible with the increased lateral variability in drumlin composition that would arise from the occurrence of linear assemblages of glacifluvial esker and subaqueous grounding line sediments in an otherwise marginal thickening till sheet

the stability of a viscous till sheet coupled with ice flow considered at wavelengths less than the ice thickness a turbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer ice is modelled as a linearly viscous fluid while the till viscosity has power law dependence on stress and effective pressure a linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till perturbation amplitude can grow this shect flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming bed features this is of great significance for large scale ice shect modelling

irish ice sheet dynamics during deglaciation of the central irish midlands evidence of ice streaming and surging from airborne lidar abstract high resolution digital terrain models dtms generated from airborne lidar data and supplemented by field evidence are used to map glacial landform assemblages dating from the last glaciation midlandian glaciation oi stages 2 3 in the central irish midlands the dtms reveal previously unrecognised low amplitude landforms including crevasse squeeze ridges and mega scale glacial lineations overprinted by conduit fills leading to ice marginal subaqueous deposits we interpret this landform assemblage as evidence for surging behaviour during ice recession the data indicate that two separate phases of accelerated ice flow were followed by ice sheet stagnation during overall deglaciation the second surge event was followed by a subglacial outburst flood forming an intricate esker and crevasse fill network the data provide the first clear evidence that ice flow direction was eastward along the eastern watershed of the shannon river basin at odds with previous models and raise the possibility that an ice stream existed in this area our work demonstrates the potential for airborne lidar surveys to produce detailed paleoglaciological reconstructions and to enhance our understanding of complex palaeo ice sheet dynamics

influence of history and environment on the sediment dynamics of intertidal flats abstract morphological trends of three distinct intertidal environments in south san francisco bay were investigated using a combination of measurement and modeling tools because of the inherent relationship between the physical environment and the sediment properties the sediment properties provide a good indicator of morphologic trends a significant finding of this study is that surface sediment erodibility increases as the energy level in the environment increases conversely subsurface sediment erodibility shows a strong relationship to the long term history of the site the combination of the measured sediment properties the history of deposition and erosion and simple modeling of the physical environment illustrate the interaction of these properties such that an understanding of intertidal flat behavior is developed

converging ice streams a new paradigm for reconstructions of the laurentide ice sheet in southern ontario and deposition of the oak ridges moraine geomorphometric analyses of high resolution 5 m digital elevation datasets shows that the greater toronto area and its immediate environs is built across the former till beds of two fast flowing ice streams the newly named the simcoe ice stream sis and the halton ice stream ois within the last laurentide ice sheet lis these formed during regional deglaciation sometime around 13 000 ybp and are directly analogous to fast flowing 3 km yr 1 ice streams in today s antarctic and greenland ice sheets their subglacial footprint in southern ontario consists of flow sets of highly elongated flow parallel till ridges up to 4 km in length and 100 m in width megascale glacial lineations msgls that converge on the oak ridges moraine orm from the north sis and south his orm is southern ontario s largest glacial landform extending from the niagara escarpment to kingston over some 160 km and was deposited as a series of en echelon glaciolacustrine fan deltas in a complexly evolving glaciolacustr

geomorphology complexity and the emerging science of the earth s surface the following is a white paper adapted here for print for the u s national research council s committee on challenges and opportunities in earth surface processes drafted at a national science foundation sponsored workshop associated with the 38th binghamton geomorphology symposium complexity in geomorphology held at duke university in october 2007

characteristics and origins of lee side stratification sequences in late pleistocene drumlins northern ireland spindle and parabolic shaped drumlins examined at fifty five localities in northern ireland possess stratification sequences on their lee side flanks these forms lack the distinctive steep stoss and tapering lee ends of classical drumlins and tend to occur in linear zones transverse to late pleistocene ice flow in most cases 90 per cent the stratified deposits infill embayments excavated in the lee side of barkhanoid forms and in the remainder 10 per cent they are superimposed on the lee side of whaleback forms the stratification sequences developed as a result of sedimentation in interconnected subglacial water filled cavities and are unlike remanie proglacial sediments moulded by ice into drumlin form stratigraphic evidence indicates that the lee side sequences developed during drumlin streamlining which supports the view that subglacial hydraulic processes played an important role in drumlin formation

pattern recognition of lidar data and sediment anisotropy advocate a polygenetic subglacial mass flow origin for the kemijarvi hummocky moraine field in northern finland abstract object based image analysis and supervised machine learning on a digital elevation model derived from airborne laser scanning data were conducted to assess the aggregate raw material potential over the kemijarvi hummocky moraine field in finnish lapland geomorphometric analysis revealed surface stoniness to be diagnostic of moraine hummocks it was utilized to detect true moraine hummocks from among the potential hummocks delineated using object based image analysis with logistic regression of curvature features derived from the digital elevation model area under the receiver operating characteristics curve auc 0 77 based on the electrical sedimentary anisotropy data the kemijarvi moraine is polygenetic such that the ridges are diagonally and erosionally fluted from sector 280 290 on their surfaces while the ridge cores are deposited from the nw from sector 310 340 the cores are composed of infill gravels and crudely stratified diamict sequences we consider the core of the kemijarvi hummocky moraine field to represent pre existing early weichselian subglacial ridges rather than being generated through monogenetic late weichselian compressional shearing and stacking frozen bed extension or bed ribbing instability mechanisms as presented for ribbed moraines that are transverse to ice flow recently evidence has been presented of multiple slip events earthquakes with moment magnitudes mw 6 7 7 0 up ice from kemijarvi we therefore propose that the genesis of the hummocks may be associated with past early weichselian fault instability within glacio isostatic adjustment s which was able to generate subglacial water bodies possibly lakes and saturated materials that were forced towards the se based on this new geomorphological evidence from mapping using a digital elevation model derived from airborne laser scanning data and azimuthal conductivity surveys combined with the reinterpretation of previously presented geophysics and sedimentological observations we suggest the kemijarvi hummocky moraine field to be reconsidered as the kemijarvi subglacial mass flow field which holds significant potential for construction aggregate materials

are drumlins a product of a thermo mechanical instability abstract of numerous theories of drumlin genesis none has been widely accepted it seems evident however that some form of positive feedback process is involved under certain circumstances perturbations are amplified herein we suggest that patchy areas of frozen bed provide the initial perturbation such frozen patches may occur in local areas underlain by material of lower thermal conductivity or on slight topographic highs drag exerted by the frozen patch deflects ice flow into its lee dragging with it mobile till eroded from the thawed area the energy balance is such that this till likely refreezes either producing a topographic perturbation or amplifying an existing one the resulting topography then deflects more of the geothermal heat away from the developing hill and into the adjacent trough resulting in a positive feedback once the thermal perturbation exceeds a critical though as yet undefined level melting may decouple the ice from the bed preventing further entrainment of till from thawed areas and thus limiting the height and length of the drumlin

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

using the size and position of drumlins to understand how they grow interact and evolve drumlins are subglacial bedforms streamlined in the direction of ice flow common in deglaciated landscapes they have been widely studied providing rich information on their internal geology size shape and spacing in contrast with bedform investigations elsewhere in geomorphology aeolian and fluvial dunes and ripples for example most drumlin studies derive observations from relict and thus static features this has made it difficult to gain information and insights about their evolution over time which likely hampers our understanding of the process es of drumlin formation here we take a morphological approach studying drumlin size and spacing metrics unlike previous studies which have focussed on databases derived from entire ice sheet beds we adopt a space for time substitution approach using individual drumlin flow sets distributed in space as proxies for different development times periods framed and assisted by insights from aeolian and fluvial geomorphology we use our metric data to explore possible scenarios of drumlin growth evolution and interaction we study the metrics of the size and spacing of 36 222 drumlins distributed amongst 71 flow sets left behind by the former british irish ice sheet and ask whether behaviour common to other bedform phenomena can be derived through statistical analysis through characterising and analysing the shape of the probability distribution functions of size and spacing metrics for each flow set we argue that drumlins grow and potentially migrate as they evolve leading to pattern coarsening furthermore our findings add support to the notion that no upper limit to drumlin size exists and to the idea that perpetual coarsening could occur if given sufficient time we propose that the framework of process and patterning commonly applied to non glacial bedforms is potentially powerful for understanding drumlin formation and for deciphering glacial landscapes

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

emergent drumlins and their clones from till dilatancy to flow instabilities subglacial bedforms are a range of landforms 10 105 m in length shaped mostly in glacial sediments and are abundant on ice sheet beds numerous explanations for their generation especially of drumlins have been proposed rather than viewing them as resulting from erosion or deposition directly by ice smalley and unwin 1968 proposed that both might occur simultaneously if beneath the glacier a layer of lubricating sediment existed and flowed conducting geomorphic work erosion deposition shaping of its own this idea appears to have steered the field leading perhaps to final resolution of the centuries old problem of drumlin genesis here i trace how the idea evolved leading to the conclusion that subglacial bedforms are emergent phenomena arising from self organisation in the coupled flow of ice sediment and water the ubiquity and patterning of bedforms appears to be well explained by a naturally arising flow instability in the subglacial system and which has been demonstrated by analytical and numerical modelling a problem for the instability theory is an apparent mismatch between predicted and observed sedimentological properties of bedforms a distinction is made between emergent drumlins drumlin clones and obstacle drumlins which helps explain some apparent contradictions and a conceptual framework is erected that might form a basis for confrontation of the theory with the wealth of observational evidence that exists

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

a unifying model for planform straightness of ripples and dunes in air and water abstract geologists physicists and mathematicians have studied ripples and dunes for more than a century but despite considerable effort no general model has been proposed to explain perhaps the most fundamental property of their morphology why are some bedforms straight continuous parallel and uniform in planform geometry i e two dimensional whereas others are irregular three dimensional here we argue that physical coupling along the crest of a bedform is required to produce straight crests and that along crest flow and sand transport provide effective physical mechanisms for that coupling ripples and dunes with the straightest and most continuous crests include longitudinal and oblique dunes in unidirectional flows wave ripples dunes in reversing flows wind ripples and ripples migrating along a slope at first glance these bedforms appear quite different ripples and dunes air and water transverse oblique and longitudinal orientations relative to the net sand transport direction but they all have one property in common a process that increases the amount of along crest sand transport that lengthens and straightens their crests relative to the across crest transport that makes them migrate and take the more typical and more three dimensional planform geometry in unidirectional flows that produce straight bedforms along crest transport of sand is caused by along crest flow non transverse bedform orientation gravitational transport along an inclined crest or ballistic splash in air bedforms in reversing flows tend to be straighter than their unidirectional counterparts because reverse transport across the bedform crest reduces the net across crest transport that causes the more typical irregular geometry relative to the along crest transport that smoothes and straightens planform geometry