Coastal processes are the most dynamic and hence most destructive. Some of the changes along the coasts take place very fast. At one place, there can be erosion in one season and deposition in another.
Most of the changes along the coasts are accomplished by waves. When waves break, the water is thrown with great force onto the shore, and simultaneously, there is a great churning of sediments on the sea bottom.
Constant impact of breaking waves drastically affects the coasts. Storm waves and tsunami waves can cause far-reaching changes in a short period of time than normal breaking waves. As wave environment changes, the intensity of the force of breaking waves changes.
Other than the action of waves, the coastal landforms depend upon:
(i) The configuration of land and sea floor;
(ii) Whether the coast is advancing (emerging) seaward or retreating (submerging) landward.
Assuming sea level to be constant, two types of coasts are considered to explain the concept of evolution of coastal landforms:
(i) High, rocky coasts (submerged coasts);
(ii) Low, smooth and gently sloping sedimentary coasts (emerged coasts).
High Rocky Coasts:
Along the high rocky coasts, the rivers appear to have been drowned with highly irregular coastline. The coastline appears highly indented with extension of water into the land where glacial valleys (fjords) are present.
As the erosion along the coast takes place a good supply material becomes available to long shore currents and waves to deposit them as beaches along the shore and as bars (long ridges of sand and/ or shingle parallel to the coast) in the near shore zone.
Bars are submerged features and when bars show up above water, they are called barrier bars. Barrier bar which gets keyed up to the headland of a bay is called a spit. When barrier bars and spits formed at the mouth of a bay and block it, a lagoon forms.
A. Erosional Landforms:
Cliffs, Terraces, Caves and Stacks:
Wave-cut cliffs and terraces are two forms usually found where erosion is the dominant shore process. Almost all sea cliffs are steep and may range from a few m to 30 m or even more. At the foot of such cliffs there may be a flat or gently sloping platform covered by rock debris derived from the sea cliff behind.
Such platforms occurring at elevations above the average height of waves is called a wave-cut terrace. The lashing of waves against the base of the cliff and the rock debris that gets smashed against the cliff along with lashing waves create hollows and these hollows get widened and deepened to form sea caves. Retreat of the cliff may leave some remnants of rock standing isolated as small islands just off the shore.
Such resistant masses of rock, originally parts of a cliff or hill are called sea stacks. Like all other features, sea stacks are also temporary and eventually coastal hills and cliffs will disappear because of wave erosion giving rise to narrow coastal plains, and with onrush of deposits from over the land behind may get covered up by alluvium or may get covered up by shingle or sand to form a wide beach.