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Glaciofluvial corridor hummocks (GCHs) within the Walker Lake map area, Canada, were examined in order to determine the character and genesis of these geomorphic features and their associated deposits. Located south of the Chantrey Moraine and north of the Keewatin Ice Divide, these corridors occur within a belt extending approximately 120 km east-west and approximately 60 km north-south. They are spaced 5-10 km apart and are hundreds of metres to several kilometres in width. They have undulating longitudinal profiles, abrupt material boundaries with the surrounding till and occur in valleys and over interfluves. Hummocks were investigated using longitudinal and perpendicular ground-penetrating radar (GPR) surveys in conjunction with pit excavations. From these analyses, the hummocks comprise a single lithofacies consisting of coarsely stratified, matrix-supported gravely sand to a depth of approximately 10 m. This sediment is similar to that of a 'sliding bed facies' observed in esker sediments and hyperconcentrated flow deposits, both of which are attributed to high meltwater discharges. Therefore, we hypothesize that the Walker Lake GCHs formed from sedimentation in cavities at the base of the ice sheet by a rapid influx of meltwater.

Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (<10 m) lenses of water perched behind ridges orientated transverse to ice flow. We show that lakes periodically drained through channels incised into bed substrate (canals). Canals sometimes trend into eskers that represent the depositional imprint of the last high-magnitude lake outburst. The subglacial lakes and channels are preserved on top of glacial lineations, indicating long-term re-organization of the subglacial drainage system and coupling to ice flow.

Government geological survey maps and research publications have portrayed the distribution of glacial landforms associated with the advance and retreat of the Laurentide and Cordilleran ice sheets across Alberta at a local, regional, and continental scale. To date, this information has not been systematically synthesized into a single compilation at a consistent scale. Although this original work provided valuable information to constrain reconstructions of former ice sheet extent, configuration, and flow geometry, its derivation primarily from the interpretation of aerial photographs and the Shuttle Radar Topography Mission 90 m digital elevation model (DEM) may result in methodological inconsistencies and spatial biases. These biases, together with challenges associated with geomorphic mapping in densely forested areas of western and northern Alberta limit the usefulness of previous mapping when applied to inversion-based ice sheet reconstructions, which have specific input data demands. Recently, light detection and ranging (LiDAR) DEMs have become increasingly available throughout Alberta. Hill-shaded imagery of these data provides unprecedented geomorphic detail beneath the forest cover and reveals that that the glacial geomorphology of northern and western Alberta is more complex than previously recognized. In this paper, we describe the methodology and geomorphic criteria used to produce a glacial landform map of Alberta using previously published data, supplemented by comprehensive new analysis of high-resolution (2-25 m) DEMs. These include 306 624 km 2 of LiDAR imagery, with which it is now possible to verify and where necessary augment previous mapping, particularly across areas with a dense forest cover.Résumé : Les cartes gouvernementales de levées géologiques et les publications de recherche décrivent la distribution de la topographie glaciaire associée à l'avance et au retrait des inlandsis laurentidien et de la Cordillère à travers l'Alberta à des échelles locale, régionale et continentale. À ce jour, cette information n'a pas été systématiquement synthétisée dans une compilation unique à une échelle uniforme. Bien que ces travaux initiaux aient fourni de bonnes informations pour encadrer les reconstructions de l'étendue des anciens inlandsis, de la configuration et de la géométrie de l'écoulement, leur provenance, basée principalement sur l'interprétation de photographies aériennes et du modèle numérique de la Mission Shuttle Radar Topography, peut engendrer des incohérences méthodologiques et des distorsions spatiales. Ces distorsions, de concert avec les défis associés à la cartographie géomorphologique dans les secteurs densément boisés de l'ouest et du nord de l'Alberta, limitent l'utilité de la cartographie antérieure lorsqu'elle est appliquée à des reconstructions d'inlandsis basées sur des inversions, lesquelles ont des exigences spécifiques d'entrée de données. Récemment, les modules d'entrée de données obtenues par détection et télémétrie par ondes lumineuses (LiDAR) sont devenus de plu...

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