The Role of Massive Ice and Exposed Headwall Properties on Retrogressive
Thaw Slump Activity
Abstract
Retrogressive Thaw Slumps (RTSs), a highly dynamic form of mass wasting,
are accelerating geomorphic change across ice-cored permafrost terrain,
yet the main controls on their activity are poorly constrained.
Questions over the spatial variability of environmentally sensitive
buried massive ice (MI) bodies and a paucity of high-spatial and
temporal resolution topographic data have limited our ability to project
their development and wider impacts. This research addresses these key
problems by investigating RTS processes on Peninsula Point — the type
site for intra-sedimental MI in the Western Canadian Arctic. Utilizing
high-resolution topographic data from drone surveys in 2016, 2017 and
2018 we (1) measure the temporal and spatial variations in headwall
properties and retreat rates, (2) determine the spatial pattern of
subsurface layering using passive seismic monitoring and (3) combine
these to analyse and contextualise the factors controlling headwall
retreat rates. We find that headwall properties, namely MI thickness and
overburden thickness, are significant controls over rates of headwall
retreat. Where persistent ice exposures are present and overburden
thickness remains < 4 m, headwall retreat is typically more
than double that of other headwalls. Furthermore, a 3D site model was
created by combining photogrammetric and passive seismic data,
highlighting the variability in internal layering, demonstrating the
limitations of extrapolations based on headwall exposures, and improving
predictions of headwall retreat rates compared to long term averages and
extrapolations from the previous year. These results provide fresh
insights into the controls on headwall retreat rates and new approaches
to improve their predictability.