GC Leong Test: Coastal Landforms - BPSC (Bihar) MCQ

• Shallow water, when it is less than the height of the waves checks their forward movement, the crests curl over and break into the shores in a mass of foam as breakers. 

• The water that finally rushes up the beach and hurls rock debris against the land is termed swash. The water is sucked back and retreats as backwash. 

• Another element in offshore drift is the undertow, which flows near the bottom away from the shore. This current exerts a pulling effect which can be dangerous to sea-bathers

• The rate of marine erosion depends on the nature of the rocks, the amount of rock exposed to the sea, the effects of tides and currents, and human interference in coast protection. 

• Other effects such as vulcanicity, glaciation, earth movement and organic accumulations have also to be considered.

• Cliffs and wave-cut platforms:  Generally any very steep rock face adjoining the coast forms a cliff. The rate of recession will depend on its geological structure: the stratification and jointing of the rocks and their resistance to wave attack. 

• If the beds dip seawards, large blocks of rock will be dislodged and fall into the sea. The cliff will rise in a series of 'steps' as shown in Fig. 75. On the contrary, if the beds dip landwards as illustrated in Fig. 76, the cliff will be more resistant to wave erosion.

• Cave, arch, stack and stump. Prolonged wave attack on the base of a cliff excavates holes in local weakness regions called caves, e.g. at Flamborough Head, England. 

• When two caves approach one another from either side of a headland and unite, they form an arch, e.g. the Neddie Eye near Wick, Scotland.

• Further erosion by waves will ultimately lead to the total collapse of the arch. The seaward portion of the headland will remain as a pillar of rock known as a stack. One of the finest examples of a stack is the Old Man of Hoy in the Orkneys which is of Old Red Sandstone and is 450 feet high.

• The waves drop the coarser materials (cobbles and boulders) at the top of the beach. 

• The finer materials (pebbles and sand grains) carried down the beach by the backwash are dropped closer to the sea. 

• On smooth lowlands, beaches may continue for miles, like those of the east coast of West Malaysia, but in upland regions where the land descends abruptly into the sea, such as the Chilean coast, long beaches are absent.

• When the ridge of shingle is formed across a river's mouth or the entrance to a bay, it is called a bar.

• The most remarkable example of a bar is Chesil Beach in Dorset, England, which extends for over 16 miles along the coast, linking the Isle of Portland with the mainland, and enclosing a lagoon called the Fleet. 

• Such a connecting bar that joins two landmasses is better known as a tombolo. 

• On the Baltic coast of Poland and Germany, large water bodies are almost completely enclosed by long bars, locally termed new rungs, to form marshy lagoons or haffs.

Fiord coasts: 

• Fiords are submerged U-shaped glacial troughs. They mark the paths of glaciers that plunged from the highlands. 

• They have steep walls, often rising straight from the sea, with tributary branches joining the main inlet at right angles. 

• Due to the greater intensity of ice erosion, fiords are deep for great distances inland, but there is a shallow section at the seaward end formed by a rock ridge and called the threshold.

Estuarine coasts: In submerged lowlands, rivers' mouths are drowned so that funnel-shaped estuaries are formed. 

• If their entrances are not silted by moving sand-banks, they make excellent sites for ports, e.g. the estuaries of the Thames, Elbe and Plate are the sites of such great seaports as London, Hamburg and Buenos Aires. 

• Tidal effects further enhance the ports' value and even when there is a little silting, modern dredges help keep the ports open all the time.

• The waves' occasional splashing against the roof of a cave may enlarge the joints when compressed air is trapped inside. 

• A natural shaft is thus formed which may eventually pierce through to the surface.

• Waves breaking into the cave may force water or spray or just air out of this hole. Such a shaft is termed a gloup or blowhole. 

• The enlargement of blowholes and the continued action of waves weaken the cave roof. 

• When the roof collapses a long, narrow inlet or creek develops. Such deep clefts, which may be 100 feet deep and equally long, are called geos, e.g. the Wife Geo, near Duncansby Head, Scotland.

Examples of uplifted lowland coasts include the south-eastern U.S.A., western Finland, eastern Sweden and parts of coastal Argentina south of the Rio de la Plata.