Evolution of an isthmus in a region of minimal relative sea level change, Calvert Island, BC central coast

The northwest coast of Calvert Island, British Columbia, hosts a large isthmus that connects two rocky headlands. Previous research suggested that its surface stabilized within the last ~500 years, but the true timing of stabilization and the origin of the isthmus were still unknown. This study used remote sensing, ground-penetrating radar (GPR), and optical dating to resolve isthmus geomorphology, stratigraphy, and structure, and to provide limiting ages, respectively, with the goal of understanding the evolution and timing of stabilization of the landform. The subsurface sedimentary architecture revealed by the GPR data, supported by a digital surface model (DSM), suggest that the isthmus began forming in the east and subsequently prograded west. The sample ages suggest that the prograding beachfaces stabilized near the surface ~600 – 700 years ago in the east, while dunes in the west stabilized ~150 years ago, however, the bulk of the isthmus is likely older.