The forces that shape coasts are (i) Erosion Caused by Sea Waves, (ii) Transportation and deposition of the rock debris, and (iii) Tectonic Forces that caused uplifts or subsidence of the coastal lands The major agent of erosion at the shoreline are sea waves. They cause erosion in four ways:
(i). Hydraulic Action: The impact force of high waves breaking against a rocky cliff during a storm can be very great. This force is enough to dislodge blocks of rocks as well as to enlarge re-existing fractures.
(ii). Abrasion: The sea waves become more destructive when they pick up rock fragments like pebbles and sands, and strike them against the cliffs. A great deal of erosion is done in this way.
(iii). Attrition: The pebbles and sands moving to and fro along with the sea waves are further broken down to smaller sizes due to mutual collision.
(iv). Chemical Action of Water: The physical destructiveness of the water is enhanced greatly by the chemical action of seawater. The chemical decays extend and widen the cracks in the rocks, and prepare them for the disintegration by waves. The chemical action of seawater is particularly seen, where coasts are composed of readily soluble rocks, such as limestones and dolomites.
Shoreline Erosional Features:
(i): Wave Cut Cliffs: The sea waves dash against the rocky shore and cut it actively. Due to continuous erosion at the base of coastal land, a cliff is formed. This cliff is called the “wave-cut cliff”.
(ii). WaveCut Bench: The sea waves undercut the cliffs and produce a notch at the base. This caused the overhanging rocks to fall into the water. In this way the cliff gradually retreats towards land, leaving a submerged rocky platform, which is called “wave-cut bench”.
(iii). Sea Arch and Sea Stack: Headlands that extend into the sea are vigorously attacked by the waves. The waves erode the rock selectively thereby destroying the softer or more highly fractured rocks at the fastest rate. At first cave-like features are produced at the base of the cliff, which is called “Sea Cave”. When two caves on opposite sides of a headland unite a gateway-like structure is formed. Such a structure is called ”Sea Arch”. When the arch falls, a pillar-like structure of the rock is left standing in the sea. Such a remnant pillar of rock is called “Sea Stack”.