Please cite this article as: Kokelj, S.V., Tunnicliffe, J., Lacelle, D., Lantz, T.C., Chin, K., Fraser, R., Increased precipitation drives mega slump development and destabilization of ice-rich permafrost terrain, northwestern Canada, Global and Planetary Change (2015), AbstractIt is anticipated that an increase in Arctic rainfall will have significant impacts on the geomorphology of permafrost landscapes. Field observations, remote sensing and historical climate data were used to investigate the drivers, processes and feedbacks that perpetuate the growth of large retrogressive thaw slumps. These "mega slumps" (5 to 40 ha) are now common in formerly glaciated, fluvially incised, ice-cored terrain of the Peel Plateau, NW Canada. Individual thaw slumps can persist for decades and their enlargement due to ground ice thaw can displace up to 10 -6 m 3 of materials from slopes to valley bottoms reconfiguring slope morphology and drainage networks. Analyses of Landsat images (1985 to 2011) indicate that the number and size of active slumps and debris tongue deposits has increased significantly with the recent intensification of rainfall. The analyses of high resolution climatic and photographic time-series for summers 2010 and 2012 shows strong linkages amongst temperature, precipitation and the downslope sediment flux from active slumps. Ground ice thaw supplies meltwater and sediments to the slump scar zone and drives diurnal pulses of surficial flow. Coherence in the timing of down valley debris tongue deposition and fine-scaled observations of sediment flux indicate that heavy rainfall stimulates major mass flow events. Evacuation of sediments from the slump scar zone can help to maintain a headwall of exposed ground ice, perpetuating slump growth and leading to larger disturbances. The development of debris tongue deposits divert streams and increase thermoerosion to initiate adjacent slumps. We conclude that higher rainfall can intensify thaw slump activity and rapidly alter the slope-sediment cascade in regions of ice-cored glaciogenic deposits.

Ice-marginal glaciated landscapes demarcate former boundaries of the continental ice sheets. Throughout circumpolar regions, permafrost has preserved relict ground ice and glacigenic sediments, delaying the sequence of postglacial landscape change that transformed temperate environments millennia earlier. Here we show that within 7 × 10 6 km 2 of glaciated permafrost terrain, extensive landscapes remain poised for major climate-driven change. Across northwestern Canada, 60-100-km-wide concentric swaths of thaw slump-affected terrain delineate the maximum and recessional positions of the Laurentide Ice Sheet. These landscapes comprise ~17% of continuous permafrost terrain in a 1.27 × 10 6 km 2 study area, indicating widespread preservation of late Pleistocene ground ice. These thaw slump, relict ground ice, and glacigenic terrain associations are also evident at the circumpolar scale. Recent intensification of thaw slumping across northwestern Canada has mobilized primary glacial sediments, triggering a cascade of fluvial, lacustrine, and coastal effects. These geologically significant processes, highlighted by the spatial distribution of thaw slumps and patterns of fluvial sediment mobilization, signal the climate-driven renewal of deglaciation and postglacial permafrost landscape evolution.

[1] Ice-cored permafrost landscapes are highly sensitive to disturbance and have the potential to undergo dramatic geomorphic transformations in response to climate change. The acceleration of thermokarst activity in the lower Mackenzie and Peel River watersheds of northwestern Canada has led to the development of large permafrost thaw slumps and caused major impacts to fluvial systems. Individual "mega slumps" have thawed up to 10 6 m 3 of ice-rich permafrost. The widespread development of these large thaw slumps (up to 40 ha area with headwalls of up to 25 m height) and associated debris flows drive distinct patterns of stream sediment and solute flux that are evident across a range of watershed scales. Suspended sediment and solute concentrations in impacted streams were several orders of magnitude greater than in unaffected streams. In summer, slump impacted streams displayed diurnal fluctuations in water levels and solute and sediment flux driven entirely by ground-ice thaw. Turbidity in these streams varied diurnally by up to an order of magnitude and followed the patterns of net radiation and ground-ice ablation in mega slumps. These diurnal patterns were discernible at the 10 3 km 2 catchment scale, and regional disturbance inventories indicate that hundreds of watersheds are already influenced by slumping. The broad scale impacts of accelerated slumping are indicated by a significant increase in solute concentrations in the Peel River (70,000 km 2 ). These observations illustrate the nature and magnitude of hydrogeomorphic changes that can be expected as glaciogenic landscapes underlain by massive ice adjust to a rapidly changing climate.

Analyses of bed load transport data from four streams in British Columbia show that the activity of mass spawning salmon moved an average of almost half of the annual bed load yield. Spawning‐generated changes in bed surface topography persisted from August through May due to lack of floods during the winter season, defining the bed surface morphology for most of the year. Hence, salmon‐driven bed load transport can substantially influence total sediment transport rates, and alter typical alluvial reach morphology. The finding that mass‐spawning fish can dominate sediment transport in mountain drainage basins has fundamental implications for understanding controls on channel morphology and aquatic ecosystem dynamics, as well as stream responses to environmental change and designing river restoration programs for channels that have, or historically had large spawning runs.

stated, in reference to the study site at Forfar 250, that "During the 1995 season, however, all tracer transport distances induced by fish were less than one channel width." Figure 3(c) shows this to be not the case. The statement should read: "…however, the average tracer transport distances induced by fish was less than one channel width."Similarly, Gottesfeld et al. (2004Gottesfeld et al. ( , p. 1078 stated that "…most of the particles (approximately 90 percent) moved more than one channel width. The pattern of movement by the nival flood and sockeye activity is similar … a large proportion of the particles moved short distances." This should be corrected to read: "…most of the particles (approximately 90 percent) moved one channel width or less."The caption for Figure 3 should be corrected to indicate that 3b is Forfar 250, 1995, 3c is Forfar 250, 1996. In Figure 3g, the labelling of nival and summer floods are reversed. The longer transport distances are for the nival flood. The dashed line style does not provide enough contrast for the reader to distinguish between summer and nival floods. Note that there is only one panel where a summer flood is indicated, and it is clearly labelled there.A discrepancy between the text and Gottesfeld et al. (2004) Figure 5 should also be corrected. The scaling ratio for depth of burial should be referred to as D flood /D fish . Therefore, the statement "To evaluate the relative burial work done by floods and fish, the B flood /B fish ratio was calculated; B flood and B fish are the mean burial by floods and fish for the year examined, respectively" (Gottesfeld et al., 2004(Gottesfeld et al., , p. 1080 should read "To evaluate the relative burial work done by floods and fish, the D flood /D fish ratio was calculated; D flood and D fish are the mean burial by floods and fish for the year examined, respectively."