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aBSTraCT. The northern Hudson Bay lowland includes the largest area of frozen peat plateau bog in Canada. Polar bear denning habitat, caribou forage, carbon storage, and wetland drainage control provided by peat plateaus will be affected if post-Little Ice age warming continues. Mapping and thermal modeling of frozen peat plateau stability indicate that permafrost peatlands are stable at a mean annual air temperature as warm as -3.5˚C. In the peat plateaus of the northern lowland, permafrost can be absent at the peat plateau margins where peat plateaus border fens or lakes. Here, insulating snow accumulations permit thawed conditions at mean annual air temperatures colder than -3.5˚C. Continued warming will result in expansion of thawed zones, subsidence at plateau margins, and even collapse of plateau surfaces, resulting in conversion to fen. This process has already occurred across north-central Manitoba, Saskatchewan, and alberta since the end of the Little Ice age, and there are signs that it is extending into the northern Hudson Bay lowland. Wave erosion of subsiding plateau borders at lake shorelines is also resulting in loss of peat plateau bog.key words: fen, Hudson Bay lowland, lake, peat plateau, peatland, permafrost, polar bear, thawing, Wapusk National Park rÉSUMÉ. Les basses-terres du nord de la baie d'Hudson comprennent la plus grande zone composée de tourbière oligotrophe de plateaux tourbeux du Canada. Advenant que le réchauffement du post-Petit Âge glaciaire se poursuive, l'habitat de tanières de l'ours polaire, les zones de fourrage du caribou, le stockage de carbone et la régulation du drainage des zones humides découlant de la présence de plateaux palsiques en subiront des conséquences. Le mappage et la modélisation thermique de la stabilité du plateau palsique gelé indiquent que les tourbières de pergélisol sont stables lorsque la température moyenne annuelle de l'air est aussi chaude que -3,5 ˚C. Dans les plateaux palsiques des basses-terres du Nord, le pergélisol peut être absent en marge des plateaux palsiques lorsque les plateaux palsiques bordent des tourbières basses ou des lacs. Ici, les accumulations de neige isolante donnent lieu à des conditions de décongélation moyennant des températures moyennes annuelles de l'air plus froides que -3,5 ˚C. Le réchauffement continu se traduira par l'agrandissement des zones de décongélation, l'affaissement à la hauteur des marges des plateaux et même l'effondrement des surfaces de plateaux, ce qui transformera ces zones en tourbières basses. Ce processus a déjà commencé à se produire dans le centre-nord du Manitoba, de la Saskatchewan et de l'alberta depuis la fin du Petit Âge glaciaire, sans compter qu'il y a des signes indiquant que cela s'étend dans le nord des basses-terres de la baie d'Hudson. L'érosion par les vagues des bordures de plateaux subsidantes à la hauteur des littoraux de lacs se traduit également par la perte de tourbières oligotrophes de plateaux tourbeux.Mots clés : tourbière basse, basses-terres de la baie d'Hudson, lac, plate...

Most spatial modelling of permafrost distribution and dynamics has been conducted at half-degree latitude/longitude or coarser resolution. Such coarse results are difficult to use for land managers and ecologists. Here we mapped permafrost distribution at 30 m × 30 m resolution for a region in the northwest Hudson Bay Lowlands using a process-based model. Land-cover types and leaf area indices were derived from Landsat imagery; peat thickness was estimated from elevation based on field measurements; and climate data were interpolated from station observations. The modelled active-layer thickness and permafrost extent compared well with field observations, demonstrating that modelling and mapping permafrost at a high spatial resolution is practical for terrains such as these lowlands. The map portrayed large variations in active-layer thickness, with land-cover type and peat thickness being the most important controlling variables. The modelled active-layer thickness on average increased by 37% during the twentieth century due to increases in air temperature and precipitation, and permafrost disappeared in some southern areas. The spatial scale of the permafrost maps developed in this study is close to that of the ecosystem and landscape features; therefore, the results are useful for land management and ecosystem assessment.

We compare surface velocities of nine rock glaciers over decadal and millennial time scales using independently derived velocities. We surveyed 15 rock glaciers in the Selwyn Mountains in 1983 and again in 1995, thereby obtaining 12-year average velocities. We also determined millennial scale velocities using lichenometric ages and rock glacier length on nine of the 15 rock glaciers for which lichenometric ages were available. The mean surveyed velocity of the nine rock glaciers was 0.20± 0.11 m/yr, and the mean age-length velocity was 0.20 ± 0.13 m/yr. A paired t-test of the two independently derived data sets shows no difference at the 0.01 level of significance. Given that both measures have inherent errors, the decadal and millennial velocities should be considered as being the same order of magnitude. The similarity of results of these two independent methods suggests that (1) decadal scale velocities of rock glaciers are comparable to millennial scale velocities in this area, and (2) either method can resolve long-term velocities.We examined surveyed velocities in relation to rock glacier characteristics in order to identify controls on velocities. Surface velocity is expected to vary with density, the sine of surface slope, thickness and temperature. Rock glaciers facing NE were significantly longer and moved faster than rock glaciers facing other directions. This may be due to greater snow, ice and debris accumulation causing increased mass. Maximum surveyed velocity was significantly correlated with rock glacier thickness (r 2 = 0.88) and with the sine of surface slope (r 2 = 0.50), when one and two outliers were excluded from analyses, respectively. Future work focusing on the systematic measurement of the dimensions, age, and velocities of rock glaciers should help to improve our understanding of controls on velocities of rock glaciers.