Massive ice and topographic controls on retrogressive thaw slump dynamics: peninsula point, western Canadian Arctic

Hayes, Sam (2020) Massive ice and topographic controls on retrogressive thaw slump dynamics: peninsula point, western Canadian Arctic. Doctoral thesis, Northumbria University.

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Abstract

Retrogressive Thaw Slumps (RTSs) — a highly dynamic form of mass wasting, are now exerting a dominant influence on geomorphic changes in the ice-cored terrain of the western Canadian Arctic. However, the main controls on their activity are poorly understood. This research aims to assess the response of RTS dominated coasts to variations in massive ice and terrain morphology. This is achieved through a multi-scale analysis of Peninsula Point — the site type for intra-sedimental massive ice. Long-term coastal change, up to 2018, is assessed using a range of metrics, including shoreline retreat (SLR) from 1935, headwall retreat (HWR) from 1994, and topographic and volumetric analysis from 2004. Inter-annual variations and fine-scale characteristics of coastal change are explored through quantitative analysis of the high-resolution structure from motion multi-view stereo data, sedimentological analysis and the novel application of passive seismic monitoring for detecting and mapping subsurface massive ice and overburden variations. Modern observations, published descriptions and historic aerial photos are used to assess changes in massive ice since 1935. Between 2016 and 2018, headwalls containing an overburden of less than 4 m in all years and an exposure of massive ice (regardless of thickness) in 2018 retreated over three times faster than other active headwalls. Furthermore, passive seismic surveys in 2017 allowed for the creation of a 3D site model, highlighting both the cross-shore and along-shore variability in the massive ice surface elevation and overburden thickness. The modelled ice closely matched subsequent observations in 2018, allowing for an accurate prediction of the relative HWR rates between 2017 and 2018. Nearshore elevation and slope display statistically significant, but weak, correlations with SLR, HWR and volume loss between 2004 and 2018, while variability in massive ice thickness and surface elevation strongly modulates both the strength and direction of these correlations. The long-term SLR rate on Peninsula Point was reduced from 5.8 m a-1 between 1935 and 1985, to 3.4 m a-1 from 1985 to 2018, in contrast with other ice-rich coasts. This disparity is explained by a thinning of the massive ice body, from widespread exposures of 5 m to 10 m during the 20th century, to patchy, thin exposures with maximum thicknesses under 5 m in recent years. The overall results have been condensed into a series of conceptual models, illustrating the coastal geomorphic response to massive ice. This research highlights how massive ice variability shapes coastal dynamics across a range of time scales, how the ice surface can be mapped by non-invasive means and the data used to improve predictions of coastal change. By allowing for more refined estimates of variability in SLR and volume loss, these findings have implications for the planning and protection of coastal infrastructure, quantifying the nutrient and sediment input to the nearshore zone and in assessing the past and future contribution of permafrost coastal change to global carbon budgets.

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