Depositional Coastal Landforms as found along the Atlantic and Gulf coasts of the United States
Depositional coasts are generally found along coast lines of gentle relief, where sediments from various sources are available. The depositional coasts are found along the Atlantic and Gulf coasts of the United States. Such coasts are influenced by the erosional processes and inundation during storms.
Characteristic wave – and current-deposited coastal landforms are the following:
Sea beach is the deposit of loose material within the reach of the waves along the shore. A beach is composed of sand, gravel, or rounded pebbles. Beaches develop on gently sloping coastal plains.
Where the wave-cut terraces are narrow, the undertow and littoral currents carry the debris from the land out into deep water to be deposited there. The beaches are built slowly away from the coast line, thus extending the land seaward.
Some beaches are broad sheets of sediments spread by waves and currents over the shore. On the contrary, there are sea beaches which resemble ridges with a crest and a steeper slope towards the land than the sea.
Beaches invariably lie between the lowest level of spring tides and the highest level reached by storm waves. A beach is generally located on a wave-cut platform of solid rock and is of low gradient with a gently concave profile.
The character of the beach deposits and the rate of accretion or removal will depend on the process of long shore drift and the composition of the surrounding coastal rocks.
Of all the depositional coastline landforms, beaches are the most familiar. Depending on the wave action along coastlines, beaches vary in type and permanence. In fact, a beach is that place along a coast where sediment is in motion.
As regards the expanse of a beach it may vary from 5 meters above high tide to 10 meters below low tide. It is to be kept in mind that beaches go through constant change especially in this era of rising sea levels.
Beaches may be classified on the basis of deposited materials on them into three types: (i) sand beaches, (ii) shingle beaches and (iii) boulder beaches.
The vertical relief of features on the sandy part of the beach is often only a few centimeters reflecting the tidal range and the slight influence of breaking waves. Runnels are small, flat- floored channels carved by low-tide runoff. They alternate with rippled surfaces and low sandy bars formed by breaking waves.
Students may be interested to have knowledge of sea beaches associated with Indian coastline.
The names of popular beaches in India are given below: Juhu beach (along Mumbai coast), Kalangut beach, Anjana and Colba beach (Goa) located along the west coast. Marina beach on Chennai coast, Puri beach (Orissa) and Vishakha-patnam beach are located on the east coast.
Beach cusps are crescent-shaped mass of sand or shingle which surround a semi-circular depression on a beach. The coarser materials are found on the horns facing seaward or promontories between the depressions.
The finer materials are deposited in bays. Beach cusps vary in size from a few centimeters to several meters in height. Giant size cusps are found on parts of the sea coast of West Africa.
They are considered to have been formed by a powerful swash and backwash action of sea waves, especially when waves are breaking directly on to the beach. The periodicity and length of the swash are closely related to the size and spacing of the cusps.
Remember that minor beach features exposed at low tide disappear during the following high tide. Beaches change form more frequently than cliffs, often over a yearly or seasonal cycle.
A bar is an elongated deposit of sand, shingle, or mud, occurring in the sea, more or less parallel to the shoreline and sometimes linked to it.
A bar which connects two coastal headlands is referred to as a bay bar. If a bar is periodically covered by tides, it is known as tidal bar. If a bar remains permanently submerged under sea water, then it is called a submerged bar.
It is a crescent-shaped beach. As the sediment from the erosion of cliff is carried by littoral drift along the sides of the bay, converging on the head of the bay, a pocket beach is formed.
One of the most common types of bar is that which is known as spit. According to Evans, a ridge or embankment of sediment attached to the land at one end and terminating in open water at the other end is known as a spit.
A spit grows from a coastline as a result of long
shore drift, often at a location where the coastline changes direction, as at the mouth of an estuary where spits are common. Many spits are considered to be product of wave refraction.
Origin of spits and Bars:
There is difference of opinion among the scholars regarding the origin of spits and bars. A brief description of their opinions has been given here.
Johnson argues that the movement and deposition of materials by long-shore currents (wave currents) are the main factor in the formation of spits. Such currents are produced by waves meeting a shore obliquely which Johnson calls shore drift.
Another view holds that for the formation of a spit it is necessary that a current passing a headland continues to follow a straight course rather than the irregularities of the coastline. An embankment will be built in the direction of movement of the current. However, changes in the current direction will account for the formation of re-curbed and other curbed forms. Recur-bed spit is also called hook spit.
Sometimes a spit is built across any stretch of water and joins Is-lands, headlands, islands and headlands. Such a spit is called a connecting bar.
A bar is called tombolo that ties islands to the mainland. In fact, tombolo is the Italian word. Tombolo forms when sediments accumulate on an underwear wave-built terrace. There is a tombolo at point Sur along the central California coast where sediment deposits connect the shore with an island.
Under special conditions opposing currents may encounter littoral currents in such a way that it leads to the landward growth of hooks until they connect with the coastline forming loops.