Ice-rich permafrost coastline erosion processes

Around the Arctic Ocean there are many stretches of coastline composed of ice-rich sediments. With the dramatic climatic, oceanic and terrestrial changes that are currently underway, there is considerable concern over the stability of these coasts and how they impact coastal communities. Unfortunately, there is still relatively little research that has been done the processes at work in these environments. Being able to effectively model coastal erosion in a permafrost setting is highly desirable. With the complexity that ice-rich permafrost conditions add to the coastal setting, modelling erosion involves a more detailed understanding of the physical and thermal conditions as well as the sedimentological and wave action processes. This research examines the rate and character of coastal erosion of ice-rich terrain and role that re-sedimentation has on the shallow water energy balance in preserving sub-bottom massive ice. It also addresses it implications to secondary sea bottom disturbance as the water depth increases.

The study area was Peninsula Point which is approximately 10 km west of Tuktoyaktuk, Northwest Territories, Canada. The massive ice and retrogressive thaw flows at this location are some of the more dramatic examples of the impact of ice-rich permafrost on coastal processes in the Arctic. Through a three decade long program of remote sensing, geophysical and ground-based monitoring, long-term changes were investigated. The character of coastal retreat above, and below, the waterline in an area where a massive ice body extends to depths below sea level were revealed. Airphoto, satellite imagery and drone data revealed the complexity of erosion with the retreating headwall of retrogressive thaw flow more rapidly eroding the landscape than the observed lateral changes of the waterline. Ground-penetrating radar (GPR) imaged the top and base of the massive ice body as well as providing a delineation of the subsurface sedimentary architecture. In winter, the GPR was pulled behind a snowmobile along transects on land, across the shoreline and out onto the near shore area of the Beaufort Sea. This provided the stratigraphic continuity between the terrestrial and sub-sea settings. The roles of erosion, re-sedimentation and shallow-water thermodynamics in the degradation and preservation of massive ground ice were revealed. The results of this study demonstrate how coastal erosion is much more complex that just the inland movement of the waterline.