What are the different Types of Coastlines?



In view of the considerable difference of opinion regarding the classification of coasts and shorelines, it is rather difficult to devise a classification that is both simple and acceptable to all.

What makes the task of classifying the coastlines difficult is the fact that only a very few present day coasts are simple in nature. On the contrary, most of the existing coastlines are compound and multi-cyclic in nature on account of changes in the sea level.

Most of the classifications of coasts and shorelines that have been proposed until today fall into two broad categories: some are purely descriptive, while others genetic.

However, while attempting any classification of coasts the following three factors must be taken into account: (i) the kind of rocks present in the coasts and their characteristics; in fact the configuration of the land bordering the sea. (ii) the major relative movement of land and sea in the recent past, and (iii) modification of the coastline, if any, by geomorphic processes.

Most of the early classifications attach considerable importance to the relative movements of land and sea. Given below is a very brief account of a few classifications proposed by eminent scholars. Davis' classification put coastlines into two broad categories: coastlines of submergence and those of emergence.

Johnson divided coasts into two major types: (i) coasts of emergence and (ii) coasts of submergence. But he added to his classification two other categories- (iii) neutral coastlines and (iv) compound coastlines At this point let it be made clear that neutral coastlines did not have the characteristics of neither emergent coasts nor submergent coasts. Rather they had independent characteristics.

Neutral coastlines comprised deltaic and alluvial plain, volcanic and coastal reef. Johnson's compound coasts possessed the characteristic features of both the submergent and emergent coastlines.

Shepard was critical of Johnson's classification and came forward with his twofold classification: (i) Primary Coastline, and (ii) Secondary Coastline. His classification being very detailed could get wide acceptance.

The most popular and simple classification proposed in recent years was that of Valentin (1952). He based his classification on the configuration types of the coast. A summary of Valentin's classification as given by Thornbury, William D. is as follows:

I. Coasts that have advanced

A. Emergent coasts

(i) Sea bottom coasts

B. Outbuilding coasts

1. Organically prograded

(a) Coral coasts

(b) Mangrove coasts

2. Inorganically prograded

(a) Marine deposition coasts

(b) Fluvial deposition coasts

II. Coasts that have retreated

A. Submergent coasts

1. Drowned glacial relief

(a) Erosional topography

(b) Depositional topography

2. Drowned fluvial topography

(a) Young folded

(b) Old folded

(c) Flat-bedded

B. Retrograded coasts

(a) Cliff-bordered

Valentin's present classification is genetic. It lays emphasis on the recent changes under­gone by the coasts. He emphasises the fact that coastal characteristics are dynamic and not static.