The coast is the shore of sea or ocean. When we use the word ‘coasts’ or ‘coastlines’, we’re referring to the zone in which coastal processes operate, or have a strong influence. The coastline includes the shallow water zone in which waves perform their work as well as beaches and cliffs shaped by waves.
Types of Coasts or Coastlines:
Despite the great variety of coastal features, coastlines may be divided into two basic types e.g. Coastlines of Emergence and Coastlines of Submergence.
(1.) Coastlines of Emergence:
These coastlines are formed due to the upliftment of the land or a fall in the sea level.
Uplifted Lowland Coast:
- The uplift of part of the continental shelf produces, a smooth gently sloping coastal lowlands.
- The offshore waters are shallow with lagoons, salt marshes, and mudflats.
- Ports that were once located on the coast become inland towns.
- Example: south-eastern U.S.A., Western Finland, eastern Sweden and parts of coastal Argentina, south of the Rio de la Plata.
Emergent Upland Coast:
- Tectonic processes may thrust up coastal plateau so that the whole region is raised with, consequent emergent features.
- A raised beach is the most prominent. The raised beach is beyond the reach of the waves through it may still possess arches, stacks, and other coastal features.
- The emergent upland cost is quite straight with cliffs and deeper offshore water.
- It has little potential for good port sites.
- Example: Scotland, the western coast of the Deccan (Malabar Coast), India and the western Arabian coast facing the Red Sea.
(2.) Coastlines of Submergence:
These coastlines formed due to the sinking of the land or the rise of the sea.
- Formed by the submergence of mountains that run right angles to the sea that is transverse or discordant to the coasts.
- A rise in the sea level submerges or drowns the lower part of the valleys to form long, narrow branching inlets separated by narrow headlands. They have been extensively used for siting fishing ports.
- Example: Typical of Atlantic type costs.
- Formed by the submergence of U-shaped glacial troughs.
- Fjords are long narrow inlets into the sea coast with more or less steep sides. Fjords form when glaciers making their way to the sea, scooped out deep trough-like valleys. When these troughs were submerged due to eustatic changes the lower end of these throughs were filled with water and become inland stretches of sea.
- Confined to the higher latitudes of the temperate regions which were once glaciated.
- Examples: Norway, Alaska, British Columbia, southern Chile and the South Island of New Zealand.
- This is the longitudinal coast where mountains run parallel or concordant to the coast. The name is taken from the coasts of Dalmatia, Yugoslavia along the Adriatic Sea.
- Where the submergence of the coastline produces long, narrow inlets with the chain of island parallel to the coast.
- It has Deep sheltered harbors but no distinguish ports.
- Examples: The Dalmatian type of coasts is also typical to the pacific coasts where the ranges are parallel to the coasts e.g. Western coast of North and South America.
- In submerged lowlands, the mouths of rivers are drowned so that funnel-shaped estuaries are formed.
- If their entrance is not silted by moving sandbank they make excellent sites for ports.
- The tidal effects further enhance the value of the ports and even when there is a little silting, modern dredges help to keep the ports open all the time.
- Examples: The estuaries of the Thames, Elbe, and Plate are the sites of many great seaports as London, Hamburg, and Buenos Aires.
According to D.W. Johnson (1919), coastlines can be divided into the following classes.
- Coastlines of Emergence.
- Coastlines of Submergence.
- Neutral Coastlines – formed as a result of new materials being built out into the water. The word ‘neutral’ implies that there need be no relative change between the level of the sea and the coastal region of the continents. Neutral coastlines include the alluvial fan-shaped coastline, delta coastline, volcano coastline, and the coral reef coastline.
- Compound Coastlines – are characterized by the evidence of both submergence and emergence. The coastline of Norway and Sweden are an example of compound coastline.
- Fault Coastlines – such coastlines were unusual features and result from the submergence of a down thrown block along a fault, such that the uplifted block has its steep side standing against the sea forming a fault coastline.