Glacial geomorphological mapping of Shuttle Radar Topography Mission (SRTM) data from the western Canadian Prairies demonstrates that during the last (late Wisconsinan) deglaciation of the Laurentide Ice Sheet terrestrial ice streams underwent a major reorganization of their fl ow confi guration. This reorganization involved a 90° shift in fl ow direction and was accompanied by a corresponding increase in the infl uence of topography on streaming fl ow. Ice streams included both topographically confi ned and "pure" ice streams that fl owed independent of topography. Streaming fl ow is recorded by suites of highly elongate (>60 km long) subglacial bedforms, bounded sharply at their lateral margins by prominent moraines. Initial streaming fl ow was unconfi ned by topography but was replaced progressively, and crosscut, by younger topographically confi ned fl ows. Flow reorganization is inferred to have been caused by temporal and spatial variations in the interaction between frozen and thawed bed conditions, with thinning and shutdown of one ice stream ultimately triggering initiation of others. This highlights the role of internal glaciodynamically driven reorganization in triggering streaming fl ow within large ice sheets and shows that large-scale fl ow reorganization can occur over the time scale of a single deglaciation in terrestrial ice streams.

Recent climate warming has activated the melt-out of relict massive ice in permafrost-preserved moraines throughout the western Canadian Arctic. This ice that has persisted since the last glaciation, buried beneath as little as 1 m of overburden, is now undergoing accelerated permafrost degradation and thermokarst. Here we document recent and intensifying thermokarst activity on eastern Banks Island that has increased the fluvial transport of sediments and solutes to the ocean. Isotopic evidence demonstrates that a major contribution to discharge is melt of relict ground ice, resulting in a significant hydrological input from thermokarst augmenting summer runoff. Accelerated thermokarst is transforming the landscape and the summer hydrological regime and altering the timing of terrestrial to marine and lacustrine transfers over significant areas of the western Canadian Arctic. The intensity of the landscape changes demonstrates that regions of cold, continuous permafrost are undergoing irreversible alteration, unprecedented since deglaciation (~13 cal kyr B.P.).

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The paper considers the forms of water movement that occur in unstratified lakes. Although not dealing directly with ecological implications, it is hoped that it will encourage the inclusion of observations of underwater weather as part of normal limnological routine. It is particularly concerned to show what observations are most effective in revealing hydraulic conditions.Relations between wind, lake geometry and wave characteristics are examined. Factors determining the steady, wind-driven circulation are reviewed and examined in sequence: the action of wind on a water surface and the current directly generated by the wind drag; the effect of the earth's rotation; the need to balance the tlow in and out of any part of the lake; the influence of lake morphometry. A simple model of lake circulation is developed that may help in the interpretation of on-lake observations. Some other features of isothermal motion are discussed including the horizontal currents associated with unsteady wind conditions (seiches).The possible interaction between waves and currents are discussed. A tentative classification of hydraulic conditions in terms of wind speed, lake depth and fetch is suggested as a basis for forming hypotheses about the motion prior to on-lake observations and as a possible starting point for a comparative approach.