Which of the following landforms is NOT considered a natural barrier?

Sea walls are human-made structures designed to protect coastlines from erosion and flooding caused by waves and tides. Unlike dunes, wetlands, and mangroves, which are natural landforms that occur in ecosystems and provide protective functions, sea walls are constructed to serve a specific purpose of coastal defense.

Dunes are formed by wind-blown sand and act as natural barriers against coastal erosion. Wetlands, which include marshes and swamps, help absorb excess water and provide habitats that can also mitigate flooding. Mangroves, found in coastal intertidal zones, offer protection against storm surges and provide vital habitats for wildlife. Each of these natural barriers plays a significant role in coastal ecology and protection, while sea walls are a designed intervention that alters the natural landscape.