Wave-cut platforms form where the sea erodes into the land. Because surf erosion cannot dig down below the base of the surf zone, a fairly level surface results, the wave-cut platform, made up of the wave-cut bench at the cliff base and the abrasion platform farther offshore. Remnant rock knobs are called chimneys.
Platforms may result from changes in sea level (eustatic changes) or changes in the elevation of the land (isostatic or tectonic changes). This gallery shows examples of both types.
Eustatic changes may leave platforms at levels above and below the current sea level. Eustatic changes related to the Quaternary ice ages are geologically rapid, and these glacio-eustatic wave-cut platforms are preserved on coasts around the world.
Isostatic platforms are found on the coasts of heavily glaciated regions. Here the land is weighed down by thick ice during glacial periods, ready to rise again when the ice melts. During this period of isostatic rebound, the newly risen sea may cut a platform early during the rebound period that emerges as the land rises.
Tectonic movements, related to the interactions of lithospheric plates, also may raise or lower a coastline, and in areas of steady tectonic uplift wave-cut platforms may be raised above the sea. This is very slow compared to eustatic and isostatic changes, and examples of tectonic platforms are few. Also, earthquake movements may temporarily lift or lower platforms, and subtle platforms may provide evidence of the regional earthquake cycle.
Fossil platforms are commonly called wave-cut terraces or marine terraces. But "terrace" has the implication of something that is built up by deposition, not carved by erosion.
- Graphic Index
- Text Index