Fundamental Drivers of Coastal Erosion
Coastal erosion occurs when the forces acting on a shoreline exceed the resistance of the materials it is composed of. The principal forces include wave action, tidal currents, storm surge, wind, ice, and precipitation-driven runoff. The resistance of a shoreline depends on the composition and strength of its sediments or rock, the presence or absence of protective vegetation, and whether natural processes like sediment supply from updrift sources are functioning.
Erosion is not inherently problematic in a purely physical sense—it is a natural process that redistributes sediment along coastlines and builds features such as barrier islands, spits, and deltas. The concern arises when the rate or spatial pattern of erosion threatens infrastructure, property, or culturally significant sites, or when it accelerates beyond the historical range of variability.
Wave Action and Storm Surge
Wave energy is the primary mechanical force driving erosion on exposed shorelines. Waves generated by wind travel across open water (fetch) and arrive at the shore carrying kinetic energy proportional to wind speed, duration, and fetch length. When waves break against a bluff or bank, they quarry material from the face, saturate the slope, and undercut the base. The resulting cantilever eventually fails and the material is incorporated into the littoral sediment budget or transported offshore.
Storm surge compounds wave action by raising water levels temporarily—sometimes by several metres during major coastal storms. Higher water means waves break directly against otherwise protected bluff faces rather than dissipating energy across a beach. The combination of storm waves and surge is typically the proximate cause of the most severe episodic erosion events along Canadian coasts.
Ice Action
Along Arctic, sub-Arctic, and Great Lakes shorelines, ice plays a significant role in erosion that has no direct equivalent on temperate ocean coasts. Thermal abrasion occurs when warm seawater or lake water melts into ice-rich permafrost or frozen shoreline material, causing the face to collapse. Ice push, in which wind drives shore ice onshore with considerable force, can scour beaches, overturn boulders, and damage structures. Ice rafting can transport large material—including boulders—offshore or to new locations along the shore.
The reduction in seasonal sea ice along the Beaufort Sea and Hudson Bay coasts, documented in satellite monitoring by the Canadian Ice Service, has extended the period during which open-water wave action can reach Arctic shores. Previously ice-protected coastlines now experience wave erosion during months when ice cover historically would have been present.
Regional Variation Across Canada
Arctic and Sub-Arctic Coasts
The Beaufort Sea coast and the shores of the Yukon, Northwest Territories, and Nunavut present some of the most rapid erosion rates documented anywhere in Canada. The Mackenzie Delta and Yukon coastal plain are underlain by ice-rich permafrost. When sea ice retreat extends the open-water season, waves erode permafrost bluffs that thaw and collapse in large segments. Natural Resources Canada's Geological Survey of Canada has produced mapping of shoreline change rates along the Beaufort Sea coast, documenting retreat at some sites exceeding several metres per year over multi-decade observation periods.
Hudson Bay and James Bay coasts are undergoing post-glacial isostatic rebound in some areas—the land is rising as it recovers from the weight of the Laurentide Ice Sheet. This means that while sea levels are rising globally, parts of northern Quebec and Ontario are rising fast enough that local relative sea level is falling. Despite this, certain soft sediment shores in these regions still experience wave-driven erosion.
Atlantic Canada
The Atlantic provinces experience a combination of sea-level rise (higher relative to the global mean along the Gulf of St. Lawrence due to the ongoing collapse of the Laurentide forebulge), storm surge from extra-tropical cyclones, and highly variable coastline geology. Prince Edward Island's red sandstone cliffs erode at rates that have been measured by successive LiDAR surveys and GPS benchmarks. The PEI Department of Environment, Energy and Climate Action maintains long-term shoreline change datasets.
The Northumberland Strait, particularly along the PEI and New Brunswick shores, has a broad shallow platform that allows storm waves to build before reaching the coast. Barrier beaches and dunes along these shores are mobile features that can migrate several metres in a single major storm.
Cape Breton's eastern coast and the Magdalen Islands (Îles-de-la-Madeleine) experience rapid erosion of soft sedimentary cliffs composed of red sandstone and glaciomarine deposits. The Magdalen Islands have been the subject of federal-provincial monitoring programmes given the threat to coastal infrastructure on an island archipelago with limited protection options.
Great Lakes
The Great Lakes are not subject to tidal forces, but their water levels fluctuate on seasonal and multi-year timescales driven by precipitation patterns, evaporation, and outflow regulation. The relationship between lake level and bluff erosion along the Ontario shores of Lake Erie and Lake Huron is well-documented. During the high-water period from approximately 2017 to 2020, bluff erosion accelerated sharply at numerous sites, leading to property losses and emergency shoreline works. The Conservation Authorities in Ontario maintain shoreline hazard mapping under the provincial Conservation Authorities Act.
Longshore sediment transport in the Great Lakes is significant. Some shores that would otherwise erode rapidly are nourished by drift from updrift erosion sites. Interrupting this transport—through the installation of jetties, breakwaters, or extensive revetments—can starve downdrift beaches of sediment supply and accelerate erosion there.
Pacific Coast
British Columbia's Pacific coast is geologically complex, with hard rock headlands, pocket beaches, fjord systems, and river-delta shores. The most erosion-sensitive areas tend to be low-lying river deltas—particularly the Fraser River delta in the Lower Mainland—and barrier beaches in the north. The Fraser delta is subsiding due to sediment compaction and has relatively low elevation, making it susceptible to storm surge and sea-level rise. Glacial isostatic adjustment rates vary across the province, affecting the relative sea-level trend at different locations.
Monitoring and Measurement
Shoreline change in Canada is monitored through several methods. Repeat LiDAR surveys from aircraft or ground-based instruments can detect changes in beach and bluff elevation at centimetre scale. Satellite imagery analysis—including the Copernicus programme operated by the European Space Agency and accessed through Canadian partnerships—provides broad-scale mapping of sediment patterns and shoreline position over time. GPS-based benchmarks at fixed locations allow precise measurement of cliff-top retreat between survey dates.
Natural Resources Canada's Geological Survey of Canada coordinates national-scale coastal monitoring, and several university research groups maintain local observation networks. The data from these programmes informs provincial shoreline hazard mapping and is used in floodplain and erosion hazard delineations required under provincial planning legislation.