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Coast and Beach

Emergent Coasts

If the coast rises, or sea level goes down, areas that were once covered by the sea will emerge and form part of the landscape. The erosive action of the waves will attack surfaces that previously lay safely below them. This wave attack occurs at sea level, but its effects extend beyond sea level. Waves may undercut a cliff, and eventually the cliff will fail and fall into the sea, removing material from higher elevations. In this manner, the cliff retreats, while the beach profile is extended at its base. The rate at which this process continues depends on the material of the cliff and the profile of the beach. As the process continues, the gradual slope of the bottom extends farther and farther until most waves break far from shore and the rate of cliff retreat slows, resulting in a stable profile that may persist for long periods of time. Eventually another episode of uplift is likely to occur, and the process repeats.

Emergent coasts, such as the coast along much of California, often exhibit a series of terraces, each consisting of a former beach and wave cut cliff. This provides evidence of both the total uplift of the coast, and its incremental nature.

Softer rocks erode more easily, leaving resistant rock that forms points of land called headlands jutting out into the sea. Subsurface depth contours mimic that of the shoreline, resulting in wave refraction when the change in depth causes the waves to change the direction of their approach. This refraction concentrates wave energy on the headlands, and spreads it out across the areas in between. The "pocket beaches" separated by jagged headlands, which characterize much of the scenic coastline of Oregon and northern California were formed in this way. Wave refraction explains the fact that waves on both sides of a headland may approach it from nearly opposite directions, producing some spectacular displays when they break.

Additional topics

Science EncyclopediaScience & Philosophy: Cluster compound to ConcupiscenceCoast and Beach - Observing Erosion And Deposition, Emergent Coasts, Submergent Coasts, The Sand Budget, Barrier Islands