Frequency and magnitude of active‐layer detachment failures in discontinuous and continuous permafrost, northern Canada

Abstract

Active‐layer detachment failures triggered weeks to months after forest fire in the central Mackenzie Valley (65°N, discontinuous permafrost zone) are compared to others generated almost immediately by summer meteorological conditions on the Fosheim Peninsula, Ellesmere Island (80°N, continuous permafrost zone). Preferred long‐axis orientations in both zones vary in relation to valley geometry and ground ice distribution: differential insolation plays no direct role in detachment failure distribution. Rates of geomorphic work over periods of one to two centuries are of the same order of magnitude. Threshold meteorological conditions for initiating failures on the Fosheim Peninsula can be incorporated into a surface heating index, but pre‐conditioning of the active layer remains important because rapid thaw does not always initiate activity. Slope pre‐conditioning does not occur at the fire‐affected sites because the failure zone is within formerly perennially frozen ground. Long‐term rates of unit vertical transport at the most active site on the Fosheim Peninsula are similar to those due to debris flow and slushflow in a nearby mountain range. The frequency of potential triggering events at the Ellesmere Island sites is expected to increase if summer climate warms, providing low percentage cloud cover is maintained during periods of high air temperatures. Copyright © 2005 John Wiley & Sons, Ltd.

Impacts of mean annual air temperature change on a regional permafrost probability model for the southern Yukon and northern British Columbia, Canada

“…The range of potential effects of climate change identified for this and other permafrost regions include warming of ground temperatures at the surface and at depth (IPCC, 2007;ACIA, 2005), increasing active layer thickness (Haeberli et al, 1993;Burn and Zhang, 2010;SWIPA, 2012;Bonnaventure and Lamoureux, 2013), basal thaw resulting in permafrost thinning (Harris et al, 2001;Woo et al, 2008), runoff changes (Woo et al, 2008), and the development of thermokarst features (Harris et al, 2001;Woo et al, 2008). Natural hazards associated with permafrost degradation (Kääb, 2008) may also develop as climate change will affect permafrost slopes, possibly generating or enhancing mass movements such as creeprelated processes, rockslides, rock falls, mudslides, and active layer detachment failures (Evans and Clague, 1994;Harris et al,2001;Lewkowicz and Harris, 2005;Dorren, 2003;Lipovsky et al, 2006;Haeberli et al, 2006;Kääb, 2008).…”

Determining the terrain characteristics related to the surface expression of subsurface water pressurization in permafrost landscapes using susceptibility modelling

“…The terrain associated with MEs include high-elevation sites, frequently on plateau or interfluve locations with low slope angles (Table 2). In contrast, ALDs are found at downslope landscape positions on low to moderate slope angles, often in areas of convergent slope drainage and topographic concavity, a pattern observed elsewhere (Lewkowicz and Harris, 2005;Rudy et al, 2016a). Hence, while surficial materials are broadly similar across CBAWO, the landscape zonation of these two features appears to follow a slope continuum.…”

“…Active MEs were also observed in 2011 and 2012 and corresponded to years with the highest mean July temperatures since 2003 at CBAWO (Holloway et al, 2016) and since 1948 when measurements began at Mould Bay, NWT (Environment Canada, 2014). ALDs and MEs occur when there is rapid thaw at the base of the active layer resulting in high PWPs and occur in similar ice-rich soil materials (Harris and Lewkowicz, 1993;Leibman, 1995;Lewkowicz and Harris, 2005;Lamoureux and Lafrenière, 2009). In the case of ALDs, these pressures lead to shear failure and downslope sliding of the active layer over the failure surface (Harris and Lewkowicz, 1993).…”

“…Landscapes composed of fine-grained surficial sediments are susceptible to a wide range of permafrost degradation processes, including the development of high PWP in the active layer (Harris and Lewkowicz, 1993;Lewkowicz and Harris, 2005). These PWPs are associated with ALDs (Lewkowicz and Harris, 2005) where soil liquid limits are exceeded.…”

“…These PWPs are associated with ALDs (Lewkowicz and Harris, 2005) where soil liquid limits are exceeded. Similarly, MEs have been documented in settings in proximity to ALDs and the occurrence of MEs is associated with deep active layer thaw and potentially with summer rainfall (Edlund, 1989;Lewkowicz, 2007;Holloway et al, 2016).…”