Offshore Bars along the Alaskan Arctic Coast

Well-developed offshore bars along the 1,355-km-long Alaskan Arctic coast possess three distinctive forms: (1) multiple parallel bars containing inner and outer bar systems; (2) long, parallel bars occurring in series but attached to the shore at their updrift ends; and (3) snorter en echelon bars attached to the shore. Some short en echelon bars are migrating to the west at a rate of 70 m yr⁻¹ and moving sediment on the order of 4 × 10⁵ m³ yr⁻¹. Bars attached to the beaches generate pronounced shoreline rhythms consisting of horns and bays with amplitudes up to 200 m and lengths of 4-5 km. Low beach-ridge and swale systems are preserved on the horns and destroyed in the bays. The bays, where the beach is narrowest, tend to coincide with locations of inlets or erosion of the tundra hinterland. Field evidence strongly indicates that variation in bar forms is related to the angle of dominant wave approach to the shore; bars tend to be shorter and more transverse to the shore where waves arrive at large angles, and longer and more parallel to the shore where waves arrive more parallel to the shore.