Abstract
Abstract. Warming of the Arctic in recent years has led to changes in the active layer and uppermost permafrost. In particular, thick active layer formation results in more frequent thaw of the ice-rich transient layer. This addition of moisture, as well as infiltration from late season precipitation, results in high pore-water pressures (PWPs) at the base of the active layer and can potentially result in landscape degradation. To predict areas that have the potential for subsurface pressurization, we use susceptibility maps generated using a generalized additive model (GAM). As model response variables, we used active layer detachments (ALDs) and mud ejections (MEs), both formed by high PWP conditions at the Cape Bounty Arctic Watershed Observatory, Melville Island, Canada. As explanatory variables, we used the terrain characteristics elevation, slope, distance to water, topographic position index (TPI), potential incoming solar radiation (PISR), distance to water, normalized difference vegetation index (NDVI; ME model only), geology, and topographic wetness index (TWI). ALDs and MEs were accurately modelled in terms of susceptibility to disturbance across the study area. The susceptibility models demonstrate that ALDs are most probable on hill slopes with gradual to steep slopes and relatively low PISR, whereas MEs are associated with higher elevation areas, lower slope angles, and areas relatively far from water. Based on these results, this method identifies areas that may be sensitive to high PWPs and helps improve our understanding of geomorphic sensitivity to permafrost degradation.
Highlights
Warm conditions during recent years in the Arctic have led to changes in the thermal, hydrological, and geotechnical properties of the seasonal active layer and the uppermost permafrost (Kokelj et al, 2002; ACIA, 2005; IPCC, 2013)
Terrain variables included in the final active layer detachments (ALDs) model were slope, elevation, potential incoming solar radiation (PISR), topographic position index (TPI), distance to water, and topographic wetness index (TWI), resulting in an explained deviance of 45 %
When reaching some threshold of pore-water pressures (PWPs), the landscape response varies depending on localized terrain characteristics, and high PWPs are expressed at the surface as ALDs or mud ejections (MEs)
Summary
Warm conditions during recent years in the Arctic have led to changes in the thermal, hydrological, and geotechnical properties of the seasonal active layer and the uppermost permafrost (Kokelj et al, 2002; ACIA, 2005; IPCC, 2013). During the fall freeze-back period this water undergoes refreezing, developing an icerich transient layer at the base of the active layer (Hinkel et al, 2001; Kokelj and Burn, 2003; Shur et al, 2005) This transient layer undergoes episodic thaw during exceptionally warm years with thick active layer formation (Shur et al, 2005). This addition of moisture, as well as infiltration from late season precipitation, results in high pore-water pressures (PWP) at the base of the active layer (Zoltai and Woo, 1978; French, 2007; Yamamoto, 2014). These pressures can lead to potentially hazardous forms of permafrost degradation and disturbance, and it is important to understand how pore-water pressurization occurs across the landscape, in relation to variable terrain characteristics
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