Rhythmic Patterns in the Shoreline Contour of the Gulf of Terpenya, Sakhalin Island

Abstract

The paper considers the results of long-term observations of megacusp (large-scale shoreline cusps) on the coast of the Gulf of Terpenya (Gulf of Patience), Sakhalin Island. The typical spatial step of the rhythmic forms is about 800 m, and the amplitude of shoreline undulations is 40–50 m. Despite significant changes on time scales of seasons, years, and decades, the main morphological features of the megacusps are preserved for more than 60 years. A model is proposed that explains the evolution of rhythmic shoreline patterns by self-organization of the bottom relief under wave impact. Development of megacusps is shown to be related to the generation of nearshore circulation cells; due to flows within the cells, a small initial perturbation to the shoreline contour can increase over time. A positive feedback between the coastal morphology and hydrodynamics arises when a certain relation is established between the length of the perturbation, the width of the surf zone, and the speeds of nearshore currents. It is concluded that the megacusp system in the Gulf of Terpenya is mainly supported by moderate waves with a significant wave height of ~1.6 m.