Multidecadal morphodynamics of a remote sand island reconstructed by LiDAR and satellite-derived bathymetry

The impacts of climate change continue to modify vulnerable environments, with disproportionate effects on small oceanic islands and coastal ecosystems. Sable Island, an isolated, narrow island near the edge of the Scotian Shelf, is entirely composed of silt and sand. The island emerged during the last deglaciation, the only remaining emergent portion of the Scotian Shelf after post-glacial sea level rise. Dynamic erosional and depositional patterns attributed to the high energy environment and unconsolidated sediment, including fluctuations in area, length, and volume, have yielded varying hypotheses of the island’s history and trajectory in over a century of investigation. Persisting gaps lead us to question how Sable Island has evolved geologically, and how do the processes that impact its modern morphology impact its future trajectory? This work focused on characterizing the modern morphodynamics of Sable Island and its nearshore by utilizing high-resolution, multi-decadal data (terrestrial and bathymetric LiDAR, airphotos, satellite imagery) to quantify terrestrial volumetric change from 2009-2024, and reconstruct nearshore bathymetric change. Quantitative (e.g., vertical change measurements from DEMs of Difference) and qualitative (e.g., visual changes in nearshore sand bars) analyses are combined to deliver preliminary results. Prominent northwest-to-southeast sediment transport patterns are shown, yielding greatest volumetric gain and loss in the island’s east end. Net coastline retreat and surface area decrease (including almost a complete loss of the east spit) paired with a slight net increase in volume over the 15-year period suggests a vertical aggradation trend that may reduce the impacts of continued sea level rise.