Sea-cliff Erosion with Rising Sea-Level along Shores Exposing Glacial Material in Atlantic Canada: The Effect of Bedrock Slope and an Example from Isle Madame, Nova Scotia

Abstract

SUMMARYRapid retreat rates of sea cliffs exposing glacial material are a widespread problem, especially in Atlantic Canada, and one that will continue. Prediction of retreat rates at specific sites involves many variables, but a factor that has commonly been overlooked in such prediction is the slope of the bedrock surface under the glacial material. A glaciated bedrock platform is generally necessary to establish a stable situation of temporary equilibrium, and as sealevel rises, the bedrock slope determines the location of the new equilibrium position. An example from Nova Scotia shows that bedrock slope is so low on some coasts that the only longrange limiting factor is kinetic, i.e. how fast hydrodynamic energy can remove glacial material. Prediction of coastal retreat scenarios requires better information on the bedrock surface than is commonly available. SOMMAIRELes taux de retrait rapide des falaises qui exposent des matériaux glaciaires est un problème très répandu et qui va perdurer, surtout dans le Canada atlantique. La prévision des taux de retrait sur des sites spécifiques comporte de nombreuses variables et, la pente du substratum rocheux sur lequel reposent ces matériaux glaciaires et une variable qui a souvent été négligée. L'existence d'un substratum rocheux glacié est généralement une condition nécessaire pour l'établissement d'une situation d'équilibre stable temporaire, et lorsque le niveau de la mer monte, la pente du substratum rocheux a une influence déterminante sur le lieu de la nouvelle position d'équilibre. Un exemple en Nouvelle-Écosse montre que la pente du substratum rocheux est si faible sur certaines côtes que le seul facteur déterminant à long terme est la ciné-tique, c'est-à-dire la vitesse d'abrasion du matériau glaciaire correspondant à l'énergie hydrodynamique. La prévi-sion des scénarios de retrait de la ligne côtière requière une meilleure connaissance du substratum rocheux.

The ‘lost’ islands of Cardigan Bay, Wales, UK: insights into the post-glacial evolution of some Celtic coasts of northwest Europe

“…Elsewhere in the North Atlantic, the exposed shore of Nova Scotia in Canada has experienced rapid erosion of cliffs in unconsolidated Pleistocene deposits, such as drumlins, with recent measured rates of 5.4 m/yr, and perhaps up to 7.6 m/yr, on the western inlet of Chezzettcook Inlet (Shaw et al 1993), and c. 8.33 m/yr through a six-year period at Cap la Ronde on Isle Madame (Force 2013). Furthermore, an island mapped offshore Nova Scotia in the eighteenth century, Fish Isle, has subsequently been removed though erosion and is "now represented only by intertidal boulder shoals" (Force 2013, p. 37), which shows a similarity to the 'lost' islands of Cardigan Bay where the Sarns, and/or associated gravel lag deposits, may be considered to be analogous to the 'boulder shoals'.…”

Integrating geomechanical surveys and remote sensing for sea cliff slope stability analysis: the Mt. Pucci case study (Italy)

“…In addition to coastal settlements, rapid landslides can be particularly dangerous for near-shore structures and infrastructure, such as oil platforms and submarine pipelines. These structures can be severely damaged by coastal landslides in both the detachment areas and the regions affected during propagation (e.g., Heezen and Ewing, 1952;Assier-Rzadkiewicz et al, 2000;Bozzano et al, 2011a;L'Heureux et al, 2011;Schulz et al, 2012;Force, 2013).…”