Homer Spit, Kachemak Bay

The Homer Spit is a 7.1 km (4.4 mi) long sand and gravel beach. The spit is formed by the southeastward movement of nearshore sediment, and a deep (200 m) submarine trough at the end acts as a sediment trap limiting further spit extension. The spit is the supra-tidal portion of a much larger subtidal feature called the Archimandritof Shoals. The shoals were initially formed as a moraine or terminal deposit when Kachemak Bay was still dominated by ancient partially grounded tidewater glaciers. Sand and gravel that now erode from sea cliffs along the Cook Inlet shoreline are suspended by turbulent storm waves, then transported by shallow water wave-induced currents, and eventually deposited where wave energy is less. The Archimandritof Shoals cause large waves to break further offshore creating a lower energy shoreline where sediment is deposited to form the spit. Changes in the volume of sediment supply can have a large impact on the stability of the spit. Earthquakes generally cause sea cliff subsidence in Cook Inlet that potentially introduces massive volumes of sediment into the nearshore leading to more accretion. Developments such as road building and seawalls or bulkheads built along naturally eroding bluffs can drastically reduce the volume of sediment transported and eventually cause more erosion. Much of the Homer Spit and the adjacent mainland have been altered with bulkheads, boulder riprap, or some other shore protection structure to prevent or slow erosion. Click here to download the CoastView app and explore more of the Homer Spit and Kachemak Bay.