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The Peterborough–Trenton drumlin field and associated meltwater erosion marks (s-forms) were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet, the Algonquin event. Recent theoretical modelling of ice-sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet. Inductive testing of this hypothesis using observations in south-central Ontario forms the crux of this paper. A geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns. Such a rough interactive geometry is suggested as the bed is drumlinized, and flows responsible for drumlins may be expected to have eroded similar forms into the ice base. Three landforms in south-central Ontario; namely tunnel channels, megachannels, and late-stage sheet-flow scours, are described, and interpreted as evidence of progressive channelization and flow diversion processes, governed by the geometric interactions between the recoupling ice base and its bed and thermodynamic feedbacks within an increasingly discontinuous meltwater sheet. Some fields of transverse ridges within tunnel channels may record meltwater deposition towards the end of the Algonquin event. By contrast, eskers within tunnel channels record a return to seasonally driven meltwater drainage. The Dummer Moraine and the Oak Ridges complex are integrated into a new landform–vent sequence for south-central Ontario which provides a framework for further field testing.

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During the decay of the Cordilleran Ice Sheet 10 000 -13 000 BP, glacial lakes developed within valleys that dissect the Interior Plateau of British Columbia. In this paper, we (1) illustrate a procedure for assessing paleo water planes that has general application, (2) document lake paleogeography and evolution in the Thompson Valley, (3) provide new data on the glacio-isostatic response of the central Cordillera, and (4) present new evidence of its late-glacial environment. We employ geomorphology and sedimentology, digital elevation models, and new technologies (differential global positioning systems, ground penetrating radar, and geographic information systems) to refine paleogeographic reconstructions of glacial lakes. Glacial Lake Thompson and Glacial Lake Deadman were ribbon-shaped (width to length ratio ≈ 3:100), deep (>>140 to -50 m) lakes that contained significant water volumes (84-24 km 3 ). They lengthened to the west and their water level lowered as ice decayed. Final ice dam failure resulted in an -20 km 3 jökulhlaup that eroded bedforms and deposited flood eddy bars within the lake basin, travelled -250 km along the Fraser River system, and may have deposited exotic mud offshore between 10 190 and 11 940 BP. Glacio-isostatic tilts of water planes are among the highest in the world (1.7-1.8 m km -1 ). Their orientations suggest that ice sheet loads were greater or longerlived to the north-northwest of the study area, lending support to the notion of an ice divide centred on the Fraser Plateau.Résumé : Durant la décroissance de l'inlandsis de la Cordillère, 10 000 -13 000 ans avant le présent, des lacs glaciaires se sont développés dans des vallées qui recoupent le plateau intérieur de la Colombie-Britannique. Dans le présent article, nous (1) décrivons une procédure d'application générale pour évaluer les paléonappes d'eau, (2) documentons la paléogéographie et l'évolution des lacs dans la vallée de la rivière Thompson, (3) fournissons de nouvelles données sur la réponse glacio-isostatique de la cordillère centrale et (4) présentons de nouvelles évidences de son environnement tardi-glaciaire. Nous utilisons la géomorphologie et la sédimentologie, des modèles numériques d'élévation et des nouvelles technologies (systèmes de positionnement global différentiels, géoradars et systèmes d'information géographi-ques) pour préciser les reconstructions paléogéographiques des lacs glaciaires. Les lacs glaciaires Thompson et Deadman avaient une forme rubanée (rapport largeur à longueur~3:100), ils étaient profonds (>> 140 à~50 m) et ils contenaient des volumes d'eau importants (84-24 km 3 ). Ils s'allongeaient vers l'ouest et leur niveau d'eau s'abaissait au fur et à mesure de la fonte de la glace. Une rupture finale de la digue de glace a causé un jökulhlaup~20 km 3 qui a érodé les fonds rocheux et a déposé des barres de tourbillons de crue dans le bassin du lac; cette masse d'eau s'est déplacée sur~250 km le long du système de la rivière Fraser et aurait pu avoir déposé des boues exotiques au large entre 1...

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