砂州は砂嘴が延伸したものか？

抄録

Sandbars and sand spits are commonly misconstrued features within coastal geomorphology. Prevailing misconceptions suggest that sandbars are merely extensions of sand spits, stretching toward the opposite shore under the influence of littoral transport. Contrary to this belief, sand spits, upon formation, serve as barriers to open sea waves, fostering a sedimentary environment on their leeward side. Wave refraction around the sand spit induces a curvature in the littoral transport direction, leading to the spit’s convex shape towards the open sea. Sandbars, in contrast, typically exhibit a concave configuration. Sand spits predominantly occur along coastlines with unidirectional sand drift, such as strait coasts, bay sides, and areas leeward of islands. They are not found on open coasts with extensive shorelines facing the sea directly, nor at the heads of bays. This absence may be attributed to the inconsistent direction of littoral drift in such locales. Conversely, sandbars are more frequently associated with open coasts and bay head areas. In Mie Prefecture, along the Ria coast of Kumano-nada, numerous small bays are flanked by capes, resulting in negligible littoral drift within these bays. Consequently, this region lacks sand spits yet features an abundance of sandbars. These observations support the assertion that coastal dynamics do not substantiate the process of sand spits evolving into sandbars.