Terrain controls on the occurrence of coastal retrogressive thaw slumps along the Yukon Coast, Canada

Abstract

Retrogressive thaw slumps (RTSs) are among the most active landforms in the Arctic; their number has increased significantly over the past decades. While processes initiating discrete RTSs are well identified, the major terrain controls on the development of coastal RTSs at a regional scale are not yet defined. Our research reveals the main geomorphic factors that determine the development of RTSs along a 238 km segment of the Yukon Coast, Canada. We (1) show the current extent of RTSs, (2) ascertain the factors controlling their activity and initiation, and (3) explain the spatial differences in the density and areal coverage of RTSs. We mapped and classified 287 RTSs using high‐resolution satellite images acquired in 2011. We highlighted the main terrain controls over their development using univariate regression trees model. Coastal geomorphology influenced both the activity and initiation of RTSs: active RTSs and RTSs initiated after 1972 occurred primarily on terrains with slope angles greater than 3.9° and 5.9°, respectively. The density and areal coverage of RTSs were constrained by the volume and thickness of massive ice bodies. Differences in rates of coastal change along the coast did not affect the model. We infer that rates of coastal change averaged over a 39 year period are unable to reflect the complex relationship between RTSs and coastline dynamics. We emphasize the need for large‐scale studies of RTSs to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget.

Monitoring Inter- and Intra-Seasonal Dynamics of Rapidly Degrading Ice-Rich Permafrost Riverbanks in the Lena Delta with TerraSAR-X Time Series

“…This prevents the development of thermo-erosional niches and consequently the rapid erosion by block collapse that is an important component at other Arctic riverbank and coastal cliff systems [11,14,17]. Given that the cliff top is decoupled from the thermo-erosional processes of the Lena River, its erosion likely results from atmospheric forcing and depends on the local sediment and ground ice properties [55], as well as regional climatic conditions [4]. This link explains the relatively gradual thermo-denudation at the cliff top.…”

Contribution of Coastal Retrogressive Thaw Slumps to the Nearshore Organic Carbon budget along the Yukon Coast

“…The size of the observed RTSs is one reason behind such differences: most of the RTSs examined in the above studies are classified as mega slumps (> 0.5 ha). RTSs along the Yukon coast are small, with an average size of 0.2 ha (Ramage et al, 2017). Furthermore, our estimates do not 25 include all of the material eroded by the RTSs; they only represent the amount of material released to the nearshore zone through slumping.…”

“…Lantuit and Pollard (2008) showed that the number of RTSs on Herschel 15 Island increased by 61% between 1952 and 2000. RTSs develop following changes that affect geomorphic settings (Ramage et al, 2017;Kokelj et al, 2017) and are induced by climatic conditions -such as increased air temperature (Lacelle et al, 2010), precipitation events (Kokelj et al, 2015;Lacelle et al, 2010) and storm events (Lantuit et al, 2012a;Lantuit and Pollard, 2008;Dallimore et al, 1996). Many RTSs that were stable or stabilized between 1952 and 1972 re-activated between 1972 and 2011.…”

“…RTSs present in 1972 were mapped using a series of geocoded aerial photographs from the 1970s obtained from the National Air Photo Library in Canada . The mapping methodology is explained in detail in Ramage et al (2017).…”

“…The coast is rapidly retreating (Harper, 1990): during the period 1951-2011, the average rate of coastal change was -0.7 m/yr and was characterized by decreasing erosion rates from West to East . RTSs are 5 common along the coast and mostly develop on segments with massive ground ice thicker than 1.5 m and coastal slope greater than 3.9° (Ramage et al, 2017). Dyke and Prest (1987) and the surficial sediments after Rampton (1982).…”