Landforms or topographical features produced by sea wave erosion:
(i) Sea Cliffs: The lower part of the rocks is eroded more rapidly than the upper part. This results in the formation of a hollow under the rock and with passage of time this excavation in the lower part of the rock keeps on becoming larger. The upper part of the rock is thus left projecting towards the sea. After sometime this projecting part falls into the sea under its own weight. As a result, a vertical wall is left, called a cliff. In India a number of sea cliffs are found along the Konkan coast of India.
(ii) Sea Caves: When the upper part of the coastal rock is hard and the lower part is soft the erosion is not uniform. The lower part of the rock in such circumstances is eroded much faster than the upper part. Due to differential erosion a hollow is created in the lower part of the rock. When the waves pound against this hollow, the pressure on air is also released and expands. Due to continuous compression of the air in the hollow the rocks are subjected to great pressure and they break. In this process the hollow in the lower part of the rock keeps on enlarging. With the passage of time they attain the form of caves and are known as sea caves.
(iii) Sea Arches: When a part of coast extends to some distance into the sea, waves working from opposite directions cut a passage through soft rock. In the initial stage, this passage is a narrow hole but it enlarges into a broad arch. These broad door-like features are called arches or natural bridges.
(iv) Sea Stacks: When the roof of an arch is broken by erosion or under its own weight or dies for any other reason a part of the original rock remains standing as a solitary mass. It may be rock forming the side of the arch. This type of a feature is called a sea stack. Stacks are of a number of types depending upon their shape and the nature of rocks.
