Drumlins Research Articles

Glacially-streamlined hard and soft beds of the paleo- Ontario ice stream in Southern Ontario and New York state

An extensive tract of glacially-streamlined terrain across a large part of Southern Ontario, Canada, is recognized as the footprint of the paleo-Ontario Ice Stream (OIS) within the easternmost Great Lakes sector of the last Laurentide Ice Sheet. The upstream part is a drumlinized and megagrooved ‘hard bed’ underlain by Cambro-Ordovician carbonates and sandstones. Subglacial plucking of jointed limestone on the lateral margins of drumlinized escarpment interfluves and rock drumlins generated a large flux of coarse debris within the ice base, recorded by sporadic spreads of hummocky rubble moraine. Downstream, the hard bed passes underneath a streamlined ‘soft’ bed of till-cored (‘drift’) drumlins and megaridges of the classic Peterborough and New York State drumlin fields. The boundary between the two bed types is a~10km wide ‘mixed bed’ of isolated drift drumlins resting on drumlinized rock suggesting a common erosional origin. Spatial variation in the geomorphology of ~2500 drift drumlins, indicates that megaridges are clones resulting from the erosion and dissection of larger parent drumlins. A large moraine system may mark the final collapse and melt of the ice stream, accompanying abrupt flow switching of its margin.

A case study in the New York Drumlin Field, an investigation using microsedimentology, resulting in the refinement of a theory of drumlin formation

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 décollement 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.

LiDAR-based volume assessment of the origin of the Wadena drumlin field, Minnesota, USA

The Wadena drumlin field (WDF; ~7500km2) in west-central Minnesota, USA, is bordered along its outer extremity by the till-cored Alexandria moraine marking the furthest extent of the southwesterly-flowing Wadena ice lobe at c. 15,000kyr BP. Newly available high-resolution Light Detection and Ranging (LiDAR) data reveal new information regarding the number, morphology and extent of streamlined bedforms in the WDF. In addition, a newly-developed quantitative methodology based on relief curvature analysis of LiDAR elevation-based raster data is used to evaluate sediment volumes represented by the WDF and its bounding end moraine. These data are used to evaluate models for the origin of drumlins. High-resolution LiDAR-based mapping doubles the streamlined footprint of the Wadena Lobe to ~16,500km2 increases the number of bedforms from ~2000 to ~6000, and most significantly, reclassifies large numbers of bedforms mapped previously as ‘drumlins’ as ‘mega-scale glacial lineations’ (MSGLs), indicating that the Wadena ice lobe experienced fast ice flow. The total volume of sediment in the Alexandria moraine is ~71–110km3, that in the drumlins and MSGLs is ~2.83km3, and the volume of swales between these bedforms is ~74.51km3. The moraine volume is equivalent to a till layer 6.8m thick across the entire bed of the Wadena lobe, suggesting drumlinization and moraine formation were accompanied by widespread lowering of the bed. This supports the hypothesis that drumlins and MSGLs are residual erosional features carved from a pre-existing till; swales represent ‘missing sediment’ that was eroded subglacially and advected downglacier to build the Alexandria Moraine during fast ice flow. Alternatively, the relatively small volume of sediment represented by subglacial bedforms indicates they could have formed rapidly by depositional processes.

Esker systems in the Gulf of Bothnia

Eskers, straight-to-sinuous ridges of waterlain sand and gravel, and their erosional meltwater channel counterparts are geomorphological imprints of the palaeo-glacial hydrological system. Esker networks hundreds of metres to hundreds of kilometres long are widespread features of Quaternary glaciations and are used to reconstruct regional and continental patterns of deglaciation. However, they have been less commonly reported from sedimentary marine environments. Esker systems from the southern Gulf of Bothnia are imaged with unprecedented clarity in new multibeam datasets which reveal a highly connected subglacial hydrological network and its relationship to an underlying drumlin field. Sinuous, elongate sediment ridges thread through a drumlin field which rises from about 80 to 50 m water depth in the southern Gulf of Bothnia (Fig. 1a–i). Individual ridge segments range from 4 km long and are c. 50–200 m wide and c. 2–20 m high. They connect into much longer esker chains over 15 km long, broken only by small gaps. The longer esker paths form a broadly dendritic network, with up to fourth-order ‘tributaries’, converging southward in the direction of ice-flow. Within tributary sections, localized braiding and anabranching occur; occasionally isolated distributaries do not reconnect to the main …

Drumlins in the Gulf of Bothnia

Drumlins are relatively small, elongate hills aligned with ice-flow direction (Menzies 1979). The name drumlin originates from the Irish word druim, which means rounded hill. They are among the most widespread glacial landforms. Drumlins are often likened to half-buried eggs or inverted spoons, with one slope blunter than the other. They belong to the group of ice-flow-parallel glacial landforms that includes glacial striae, flutes, crag-and-tails and mega-scale glacial lineations. Drumlins are very common in the landscape of central and northern Scandinavia (Hattestrand 1998), but their identification in the Baltic Sea and Gulf of Bothnia has been hindered by a lack of seafloor data. Here we show a drumlin field from the southern Gulf of Bothnia. The drumlin field shown in Figure 1 stretches for >85 km and probably continues northwards beyond the coverage of the high-resolution bathymetric data available for this study. The outlines of the drumlins are generally easy to distinguish (Fig. 1c), although their surfaces are frequently scarred by iceberg ploughmarks and pits (Fig. 1e, f). The drumlins are aligned NNW–SSE (169°) and their morphology changes progressively along the mapped section. The northern part is characterized by shorter, wider drumlins, whereas …

An anisotropy of magnetic susceptibility (AMS) investigation of the till fabric of drumlins: support for an accretionary origin

This paper describes the results of a spatially dense anisotropy of magnetic susceptibility (AMS) till fabric study of a single drumlin in the Weedsport Drumlin Field, New York State, USA. AMS till fabrics provide a robust, quantitative and unbiased approach to assess subglacial till kinematics and infer ice‐flow dynamics. The drumlin selected for this detailed investigation was systematically sampled at 18 locations to evaluate the patterns of ice flow and associated till kinematics within a drumlin and to test erosional vs. depositional models for its formation. AMS till fabric analysis yielded strong fabrics that increase in strength towards the drumlin crest, indicating that bed deformation occurred during till deposition and that deformation within the drumlin was greater than that in the interdrumlin low. Fabric orientations reveal drumlin convergent, divergent and parallel ice‐flow paths that illustrate a complex interaction between ice flow and the drumlin form; fabric strength and shape reveal systematic differences in bed deformation between the interdrumlin and drumlin regions. These observations are inconsistent with purely erosional models of drumlin genesis; instead, these observations are more consistent with syndepositional streamlining of till transported, probably locally as a deforming bed, from the interdrumlin low towards the drumlin locality.

Quantifying Eroded Sediment Volume during Drumlin Formation in Simcoe County

Drumlins, despite being well studied, are still incredibly enigmatic in terms of their formation processes. Theories on their origin vary widely, and the evidence presented in this study seeks to assist in this debate. To support an erosional theory for the formation of drumlins, large volumes of sediment would have undergone transport and deposition. The volume of sediment that would have eroded from part of the Peterborough Drumlin Field in Simcoe County was calculated using two methods in a GIS. The limitations of both methods and the geological composition of potential sediment sinks were analysed. The range of eroded sediment volume was calculated to be 3.5–8.3 km3, which could fill between 30.2% and 71.6% of the Lake Simcoe basin. The high volume of sediment that was estimated in this study will have future implications in the drumlin debate and for the feasibility of an erosional process of formation.

Drumlin sedimentology in a hard‐bed, lowland setting, Connemara, western Ireland: implications for subglacial bedform generation in areas of sparse till cover

ABSTRACTCores 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.

Automated drumlin shape and volume estimation using high resolution LiDAR imagery (Curvature Based Relief Separation): A test from the Wadena Drumlin Field, Minnesota

Resolving the origin(s) of drumlins and related megaridges in areas of megascale glacial lineations (MSGL) left by paleo-ice sheets is critical to understanding how ancient ice sheets interacted with their sediment beds. MSGL is now linked with fast-flowing ice streams but there is a broad range of erosional and depositional models. Further progress is reliant on constraining fluxes of subglacial sediment at the ice sheet base which in turn is dependent on morphological data such as landform shape and elongation and most importantly landform volume. Past practice in determining shape has employed a broad range of geomorphological methods from strictly visualisation techniques to more complex semi-automated and automated drumlin extraction methods. This paper reviews and builds on currently available visualisation, semi-automated and automated extraction methods and presents a new, Curvature Based Relief Separation (CBRS) technique; for drumlin mapping. This uses curvature analysis to generate a base level from which topography can be normalized and drumlin volume can be derived. This methodology is tested using a high resolution (3m) LiDAR elevation dataset from the Wadena Drumlin Field, Minnesota, USA, which was constructed by the Wadena Lobe of the Laurentide Ice Sheet ca. 20,000years ago and which as a whole contains ~2000 drumlins across an area of ~7500km2. This analysis demonstrates that CBRS provides an objective and robust procedure for automated drumlin extraction. There is strong agreement with manually selected landforms but the method is also capable of resolving features that were not detectable manually thereby considerably expanding the known population of streamlined landforms. CBRS provides an effective automatic method for visualisation of large areas of the streamlined beds of former ice sheets and for modelling sediment fluxes below ice sheets.

The 1992 Farrington Lecture: Drumlin Bedforms and Related Ice-Marginal Depositional Systems in Ireland

The Irish drumlin bell comprises a wide morphological range of subglacial bedforms which are best developed in lowland zones located mainly in northern and western sectors of the island. Stratigraphic evidence suggests that drumlinisation occurred around 17ka B.P. in response to fast ice flow from major centres of inland ice dispersion onto the continental shelf. Well-defined moraines and morainal banks bordering the drumlin fields indicate that drumlinisation was accompanied by a high basal debris flux to ice sheet margins which was resedimented in a variety of subaquaeous settings. Field observations indicate that the fast ice flow responsible for streamlining and sediment moulding was closely associated with intense marine downdraw, a decrease in basal effective pressures and a general lowering of ice sheet profiles during deglaciation. Deglacial mechanisms of this type help to explain the very rapid termination of the last glacial cycle because downdraw ice-stream drainage basins must expand in area if pulling power lowers the surface faster than ice supply raises it. Sedimentary and structural variability within drumlins indicate that drumlin formation reflects not only a highly dynamic subglacial system but, in some cases, can be related to ice sheet history. The seven main facies associations which have been identified provide a window into a variety of depositional settings which contributed to drumlin formation and drumlinisation. They confirm that drumlins are not simple landforms but have a complex history related to changing glaciological states and ice sheet evolution. The final drumlin forms however are the result of a highly mobile flux of basal debris and meltwater directed subglacially towards ice sheet margins.

Subglacial bedforms of the Zemgale Ice Lobe, south-eastern Baltic

Presented in this paper are the results of the mapping of ∼6600 subglacial bedforms of the Zemgale Ice Lobe (ZIL), their composition and internal structure in the south-eastern Baltic region. Topographic maps at scale 1:10,000 were mainly used to map bedforms in Latvia, while a digital elevation model with cell size of 5 m was used for North Central Lithuania. The ZIL operated during the deglaciation of the Late Weichselian Scandinavian Ice Sheet (SIS), at least in the Middle Lithuanian and North Lithuanian glacial phases, and created a subglacial landform assemblage consisting of glacial lineations such as drumlins, mega-flutings, Mega Scale Glacial Lineations (MSGLs) and transversal morphologies, such as ribbed moraines. It is observed that lineations of different scales co-exist, suggesting subglacial bedform transition and possibly a continuum of bedforms. Highly elongated lineations with a length of up to 24 km and an elongation ratio of up to 1:50, interpreted as MSGLs, are observed in the NE part of the Middle Lithuanian Plain. In the so-called Zemgale drumlin field, 20% of lineations have elongation ratios >10:1, indicating the fastest ice flow in the central part of the main body of the lobe. Based on test surveys and investigated outcrops, the drumlin cores consist of sorted sediments with different levels and depths of glaciotectonic deformation overlain by subglacial till. The main drumlin-forming ice stress was mostly parallel to the crests of drumlins, while some ice stress from inter-drumlin depressions acted during the final episodes of their formation. The observed sediment structures indicate multiple episodes of the basal ice/bed coupling and decoupling, which can best be explained by the mosaic ice-bed deformation model. Ribbed moraines are characterized by a complicated structure of multiple till units interbedded with sorted sediments that have been formed by repeated subglacial overthrusting.

The drumlin field and the geomorphology of the Múlajökull surge-type glacier, central Iceland

Here we present a new geomorphological map of the active drumlin field and the forefield of Múlajökull, 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 Múlajökull 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. However, the large number (i.e., 110) of drumlins forming the drumlin field is unique for modern Icelandic surge-type glaciers and, as yet, unique for contemporary glaciers in general. Also apparent is that the drumlins are wider and 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 Múlajökull.

Quantitative geomorphological analysis of drumlins in the peterborough drumlin field, ontario, canada

Drumlins are enigmatic subglacial landforms that have been interpreted to form by a number of processes, including incremental accumulation of till, erosion of previously deposited sediment, catastrophic meltwater floods, and sediment deformation. However, relatively little is known about the controls on drumlin formation, such as spatially variable glacial processes or substrate characteristics, and how these controls may be identified from variations in drumlin morphology within a single drumlin field. This paper explores a computational method that allows identification of drumlins and extraction of their morphological characteristics from existing topographic digital data for a portion of the eterborough drumlin field in ntario, anada. Spatial and non‐spatial analysis of the form and distribution of drumlins across the study area identifies drumlin characteristics such as size, elongation ratio, symmetry and long axis orientation and shows that drumlins are not randomly distributed across the region and their form characteristics have distinct regional trends. Kernel density analysis is used to identify the regional trends in drumlin characteristics. Factors that appear to influence the form and distribution of drumlins in the study area include sediment thickness, length of time beneath the ice, ice velocity and direction of ice movement. The distribution of particularly well developed asymmetric and elongate drumlins coincides with the location of a broad bedrock low and is interpreted to identify the former location of a fast‐flowing ice stream.

Subglacial sediment, proglacial lake-level and topographic controls on ice extent and lobe geometries during the Last Glacial Maximum in NW Russia

Investigations in sections along the rivers Severnaya Dvina and Vaga, and morphological mapping based on a new digital elevation model and Landsat imagery, allow for a reinterpretation of the extent of the Scandinavian Ice Sheet during the Last Glacial Maximum (LGM). The reconstruction provides a much better link between stratigraphical and morphological expression of glaciation than previous proposals. Most striking is the configuration of long, low-gradient ice-lobes (ice-streams) extending for some 300–400 km up the wide and smooth river valleys. Their extremely low surface gradients are evidenced by glacial trimlines that formed along the sides of the ice-lobes in contact with the gentle valley slopes. In the main valleys, end moraines marking terminal positions are present, whereas drumlins are rare in the peripheral areas of the ice sheet but found in some tributary valleys at somewhat higher elevations. Large drumlin fields, however, are found farther up-ice. The glacial sediment succession is composed of waterlain sediments and tills. The sediments provide evidence of distal ice damming, glacier overriding and retreat, and finally distally glaciolacustrine sedimentation and lake drainage. The diamicton unit associated with the LGM shows evidence of basal coupling, although more striking is the abundant evidence for ice–bed decoupling. These include in situ waterlain sediments within tills, and clastic sills running along the till/substrate contact showing lift-off. These features indicate that the weight of the glacier lobes was, to a large extent, carried by pore-water pressure in subglacial sediments, and that subglacial shear and erosion were moderate. Thus, fast ice flow in the lobes is envisaged. The balance between glacier weight and pore-water pressure was probably maintained over time by the buoyancy effect of glaciers advancing into proglacial lakes. Subglacial lakes may have formed by capture of proglacial lakes during glacial advance. The combination of low-gradient ice and decoupled beds indicate that glacier advance and extent was largely controlled by lake levels and topographic thresholds. This is taken to indicate that steeper-gradient ice much farther upstream was providing the gravitational push. A presumably abrupt change in ice-surface profile is supported by the mapped distribution of glacial bedforms. The model presented herein potentially has wide applicability for large parts of northern Russia as the topographic setting and glacier advance in lakes across fine-grained low-permeable sediments provide very similar conditions.

Deglaciation chronology of the Pandivere and Palivere ice-marginal zones in Estonia

Accelerator mass spectrometry (AMS) 14 C dates, pollen and plant macrofossil evidence and lithostratigraphic parameters obtained from four Late Glacial lake sediment records were used to study the deglaciation chronology of Estonia. AMS dates show that the northern part of the Saadjarv Drumlin Field was free of ice cover at approximately 14 300–14 200 cal yr BP. These ages fit well with the ice retreat estimations (14 700–14 500 cal yr BP) of the Otepaa ice-marginal zone in the south and the deglaciation of the Pandivere Upland in the north (13 800 cal yr BP). Glaciolacustrine sediments of the Haljala and Udriku basins were deposited in proglacial lake A 1 , a northeastern bay of the Baltic Ice Lake that already existed ca . 13 800 cal yr BP. The Palivere ice-marginal zone, and proglacial lake A 2 associated with it, was formed ca. 500 years later, at approximately 13 200 cal yr BP. New evidence indicates that ice readvance during the Palivere stade terminated during the Allerod chronozone.

Glacial landsystems and dynamics of the Saginaw Lobe of the Laurentide Ice Sheet, Michigan, USA

The surficial terrain of the Saginaw Lobe in southern Michigan is divided into 4 landsystems, numbered sequentially from southwest to northeast, containing related assemblages of sediments and landforms, two of which appear to have a genetic relationship with the bedrock units over which they lie. Landsystem 1 consists of the Sturgis Moraine, a terminal/recessional moraine, and an adjacent drumlin field. The moraine is a high-relief ridge with hummocky topography and ice-walled lake plains at its crest, and thick, coarse outwash fans on its distal margin. The drumlin field extends up-glacier from the Sturgis Moraine across the subcrop of the Mississippian Coldwater Shale to the subcrop of the overlying Marshall Sandstone. The low permeability of the shale may have increased basal pore pressures into a range in which deformation of basal sediment into drumlins occurred. Landsystem 2 overlies the subcrop of the Marshall Sandstone. Stagnation of the lobe behind a discontinuous moraine in this area is indicated by high relief, collapse topography, composed of kames, eskers, and ice-walled lake plains. A system of tunnel valleys terminates and merges in this landsystem with large outwash fans and plains sloping away from the margin. High basal drainage into the sandstone may have facilitated stagnation across a broad area to form this landsystem. Landsystem 3 may have also developed during stagnation of the lobe, but it differs from landsystem 2 by its more subdued relief. It contains a network of evenly spaced, southwest-trending open tunnel valleys that contain discontinuous esker segments. Landsystem 4 consists of till plains and low recessional moraines formed as the Saginaw Lobe retreated downslope into Saginaw Bay of the Lake Huron Basin. Tunnel valleys are absent in this area.

Exploring till bed kinematics using AMS magnetic fabrics and pebble fabrics: the Weedsport drumlin field, New York State, USA

Gentoso, M. J., Evenson, E. B., Kodama, K. P., Iverson, N. R., Alley, R. B., Berti, C. & Kozlowski, A. 2012 (January): Exploring till bed kinematics using AMS magnetic fabrics and pebble fabrics: the Weedsport drumlin field, New York State, USA. Boreas, Vol. 41, pp. 31–41. 10.1111/j.1502‐3885.2011.00221.x. ISSN 0300‐9483.Thick, relatively homogeneous basal tills exposed in the drumlins and flutes of the Weedsport drumlin and flute field in New York State exhibit anisotropy of magnetic susceptibility (AMS) and pebble fabrics that are consistently oriented parallel to the streamlined bedforms. The pebble fabrics and AMS fabrics are concordant. In this study, six drumlins and five flutes were sampled. Thermally induced, incremental reduction of isothermal remanent magnetization indicates that AMS is caused by primarily elongate maghaemite grains. The orientations of principal axes of maximum susceptibility (k1) are generally parallel to pebble long‐axis orientations, and tend to plunge mildly up‐glacier. Fabric directions are generally parallel to drumlin long‐axis orientations, but deviate by 12°–23° from flute directions. Fabrics of the flutes are stronger and more unidirectional than those of the drumlins. These results support the use of AMS as a fast and objective method for characterizing fabrics in tills, and suggest hypotheses about basal processes linked to glacially streamlined landforms.

An object-oriented approach to automated landform mapping: A case study of drumlins

This paper details an automated object-oriented approach to mapping landforms from digital elevation models (DEMs), using the example of drumlins in the Chautauqua drumlin field in NW Pennsylvania and upstate New York. Object-oriented classification is highly desirable as it can identify specific shapes in datasets based on both the pixel values in a raster dataset and the contextual information between pixels and extracted objects. The methodology is built specifically for application to the USGS 30 m resolution DEM data, which are freely available to the public and of sufficient resolution to map medium scale landforms. Using the raw DEM data, as well as derived aspect and slope, Definiens Developer (v.7) was used to perform multiresolution segmentation, followed by rule-based classification in order to extract individual polygons that represent drumlins. Drumlins obtained by automated extraction were visually and statistically compared to those identified via manual digitization. Detailed morphometric descriptive statistics such as means, ranges, and standard deviations were inspected and compared for length, width, elongation ratio, area, and perimeter. Although the manual and automated results were not always statistically identical, a more detailed comparison of just the drumlins identified by both procedures showed that the automated methods easily matched the manual digitization. Differences in the two methods related to mapping compound drumlins, and smaller and larger drumlins. The automated method generally identified more features in these categories than the manual method and thus outperformed the manual method.

A glacial geomorphological map of the Seno Skyring-Seno Otway-Strait of Magellan region, southernmost Patagonia

Please click here to download the map associated with this article. This paper presents a detailed glacial geomorphological map covering over 16,000 km of the Seno Skyring-Seno Otway-Strait of Magellan region in southernmost Patagonia. It builds on previously published maps produced at a variety of scales and is re-mapped in detail for the purposes of reconstructing the pre-Last Glacial Maximum (LGM) glacial dynamics of the region, with particular focus on deciphering the glacial landsystem north east of Seno Otway, which has been postulated as a zone of ice streaming. Additional areas of interest include the reconstruction of proglacial lakes dammed by the Skyring and Otway lobes; their drainage during various stages of retreat; and a landsystems approach to the overall reconstruction of the combined Skyring-Otway-Magellan ice lobes. Mapping was conducted using a combination of Landsat ETM+ and ASTER satellite imagery and oblique and vertical aerial photographs, and is centred on approximately 53_S, 71_W. Seven main landform types have been mapped: glacial lineations, moraines, meltwater channels, irregular dissected ridges, eskers, outwash plains and former shorelines. The map records several episodes of ice flow, as revealed by glacial lineations, with the area around Laguna Cabeza del Mar exhibiting spectacular elongate drumlins. Drumlin fields are associated with three major ice lobes whose extent is marked by a series of moraine ridges and lateral meltwater channels. Large parts of the area were also subjected to proglacial meltwater erosion and deposition, as recorded by large tracts of outwash and associated channels.

Sedimentary bodies, forms and occurrences in the Tudorevo and Mirovo glacial deposits of northern Velebit (Croatia)

A small glacier of cirque-valley type existed during the Late Pleistocene Wurm Glacial in the Tudorevo and Mirovo karst valleys of Northern Velebit. Its source was in Tudorevo, and it moved through Dundovic Mirovo and Bilensko Mirovo to Baricevic Dolac, shaping U-valleys around 4 km in length. After melting, glacial deposits remained, composed of chaotic and unsorted till, composed of carbonate sand, debris and sub-rounded clasts, cobbles and blocks of predominantly Middle Jurassic and subordinately Lower Jurassic carbonate rocks. In Dundovic Mirovo and Bilensko Mirovo, where the largest masses of glacial deposits occur, terminal and recessional moraines can be found over the ground moraine, as well as some other features, mostly drumlins (drumlin field), eskers, erratic blocks, kettle holes and striations. Some erratics have been transported for more than 4 km from their primary outcrops, e.g. clasts of Lower Jurassic Toarcian Spotty limestone. A terminal moraine was deposited between Bilensko Mirovo and Baricevic Dolac, perpendicular to the glaciated U-valley and it forms the Bilo hill, the northern and southern foothills of which are composed partly of glaciofluvial deposits. Between Tudorevo and Mirovo, a recessional moraine occurs above the ground moraine. The glacier was subject to polyphase melting and freezing, and the youngest freezing events may be related to cirques in Tudorevo. During melting events, glacier lakes are supposed to have existed, initially in the Baricevic Dolac, later in Mirovo area and finally in Tudorevo. These discharged into the karst underground by percolation through till and by erosion to the karstified underlying Middle Jurassic carbonates.