Which of the following landforms are produced on coastal area by wave erosion ?

Question

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Correct — option (1), Sea cliff, Bay, Sea caves, Sea stacks. Every landform in that group is cut out of the land by the sea rather than built up by it, and the sequence in which they form is a single connected story. Waves attack the base of a shore where it meets resistant rock, working by hydraulic action as compressed air is driven into joints, by abrasion as the water hurls sand and shingle against the rock face, by attrition as those fragments grind each other down, and by solution where the rock is soluble. The first result is a notch at the level of wave attack. As the notch deepens, the rock above it is undermined and collapses, and repeated collapse drives the shore backwards as a steep sea cliff, leaving a wave-cut platform sloping seaward at its foot. Where the cliff is jointed or faulted, the waves exploit the weakness and hollow out a sea cave. Where caves are cut into both sides of a projecting headland and meet, the result is an arch; when the roof of the arch falls in, the seaward remnant is left standing as an isolated sea stack, and continued attack reduces the stack to a stump awash at high tide. The bay belongs to the same erosional family by a different route. Where a coast is made of alternating bands of harder and softer rock lying across the shoreline, the sea cuts back the weak bands much faster than the resistant ones, so the soft bands become curved indentations while the hard bands are left protruding — that is differential erosion, and it produces the alternating headlands and bays that give a rocky coast its outline. Because wave energy then converges on the headlands and spreads out in the bays, the headlands take the continuing attack and the bays become quieter water where deposition can begin. That last point is what makes coastal geomorphology confusing and examinable: erosion and deposition operate along the same stretch of coast at the same time, and a candidate has to know which process produced which specific form.

Why the other options are wrong — (b) Only the first item here is erosional. A wave-built terrace is the ramp of sediment laid down in deeper water at the seaward edge of the wave-cut platform, built from the debris the waves have removed from the cliff, and its name is the trap — a wave-cut terrace or platform is erosional, a wave-built terrace is depositional, and the two are separated by one word. Sand bars are ridges of sediment thrown up by waves and longshore drift across a bay mouth or offshore, and a lagoon is the sheet of shallow water enclosed behind such a bar or a spit, so both are consequences of deposition. This choice is in effect a list of depositional features with one erosional item at the front to make it look plausible.  (c) The first two are erosional and the last two are not. Lagoons and sand bars are the classic products of coastal deposition: waves and the longshore current carry sediment along the shore, drop it where the coast changes direction or where wave energy falls, and build a spit or a bar which eventually seals off a body of water behind it. The Chilika lagoon in Odisha, Pulicat between Andhra Pradesh and Tamil Nadu and the Vembanad backwater in Kerala are the Indian examples worth carrying. This choice will tempt a candidate who groups landforms by where they occur rather than by how they are made, since all four are unquestionably coastal.  (d) This is the near-miss and the choice most likely to cost a mark. Three of its four items are the same erosional forms the key names, and it fails on the lagoon alone. A lagoon is water impounded behind a bar, a spit or a reef and therefore exists only because sediment has been deposited across the entrance to a bay; no amount of wave erosion produces one. The lesson is to check every item in a list-type option rather than stopping when a pattern looks established, because an examiner who wants to separate the careful candidate from the quick one will build the near-miss by changing exactly one item in the correct list.

Concept: Coastal landforms divide cleanly into two families once the question asked is where the material went. Erosional forms are what remains after the sea has removed rock: the notch, the sea cliff, the wave-cut platform or terrace, the sea cave, the sea arch, the sea stack and the stump, the blowhole where a cave roof is pierced, and the alternation of headlands and bays produced by differential erosion of unequally resistant rock. Depositional forms are what the sea has built out of that removed material together with sediment delivered by rivers: the beach, the berm, the wave-built terrace offshore, the spit growing from a headland, the bar closing a bay, the tombolo tying an island to the mainland, the barrier island, the lagoon impounded behind a bar, and coastal sand dunes. The agent of transport along the shore is longshore drift, the zig-zag movement produced when waves approach the beach obliquely and the backwash returns straight down the slope. Coasts are also classified as emergent or submergent according to whether the land has risen relative to the sea, and India offers both — a largely emergent east coast with lagoons and deltas, and a more submergent west coast.

State PCS 2021 Q16 — Geography PYQ with Answer

State PCS 2021 Q16 — Geography PYQ with Answer