MPSC 2021 Prelims Q16: Which of the following landforms are produced on coastal

Q: What is the answer to MPSC 2021 Prelims Q16?

(1). 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.

MPSC 2021 Prelims Paper-I · Question 16 of 100

State Services Preliminary Examination 2021, held 23 January 2022. Transcribed from the commission's own booklet (संच A); answer as per the official MPSC final answer key.

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

(1)Sea cliff, Bay, Sea caves, Sea stacks
(2)Sea cliff, Wave built terrace, Sand bars, Lagoon
(3)Bay, Sea cliff, Lagoon, Sand bars
(4)Sea stacks, Sea cliff, Bay, Lagoon

Answer

(1)

Why

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 others are wrong

(2)Sea cliff, Wave built terrace, Sand bars, Lagoon — 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.
(3)Bay, Sea cliff, Lagoon, Sand bars — 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.
(4)Sea stacks, Sea cliff, Bay, Lagoon — 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.

Physical geography questions in MPSC Paper-I are usually classification questions in disguise. The commission does not often ask how a landform is made; it asks which of these belong to a stated process, which is a harder question because it requires the whole family to be sorted rather than one member to be described. The technique that answers them is to hold each landform with a one-word tag for its process — cliff, erosional; spit, depositional — and then to read every item in every choice rather than the first two. The Indian coastline supplies the examples the commission likes to attach: the lagoons of the east coast at Chilika and Pulicat, the Kerala backwaters, the cliffs and stacks of the Konkan and the Malabar coast, and the sandy beaches of Maharashtra's own shoreline. Maharashtra's coast in particular runs along a submerged and rocky margin with headlands, small bays and cliffed sections, which is why a coastal-erosion question is natural material for this commission.

Key facts

Waves erode by hydraulic action, abrasion or corrasion, attrition and solution; the first product on a rocky shore is a notch at the level of wave attack, which undermines the rock above and produces a receding sea cliff with a wave-cut platform at its foot.
The sequence cave, arch, stack, stump describes the progressive destruction of a headland: caves cut on both sides meet to form an arch, the arch roof collapses to leave a stack, and the stack is reduced to a stump.
Bays are erosional in origin where a coast is made of alternating resistant and weak rock lying across the shoreline; the weak bands are cut back faster, leaving the resistant bands as headlands.
A wave-cut terrace or platform is erosional, whereas a wave-built terrace is the depositional ramp of sediment laid down seaward of it — the two differ by a single word in the name.
Sand bars, spits, tombolos, barrier islands and lagoons are depositional; Indian examples of coastal lagoons include Chilika in Odisha, Pulicat between Andhra Pradesh and Tamil Nadu and the Vembanad backwater in Kerala.

Sort every coastal landform by where the material went, not by where the feature sits

Sea cliff→EROSIONAL — waves attack by hydraulic action, abrasion, attrition and solution, and cut a notch at the level of attack. The rock above is undermined and collapses; repeated collapse drives the shore backwards as a steep cliff, leaving a wave-cut platform sloping seaward at its foot

Sea cave, and after it arch, stack, stump→EROSIONAL — the progressive destruction of a headland. Waves exploit joints and faults to hollow out a cave; caves cut into both sides of a projecting headland meet as an arch; the arch roof falls in and the seaward remnant is left standing as an isolated stack; continued attack reduces the stack to a stump awash at high tide

Bay→EROSIONAL — where a coast is made of alternating harder and softer bands lying across the shoreline, the sea cuts back the weak bands much faster than the resistant ones. That is differential erosion: the resistant bands are left protruding as headlands and the weak bands become the curved indentations between them

Wave-built terrace→DEPOSITIONAL — and one word away from an erosional form, which is the whole trap. A wave-CUT terrace or platform is what erosion leaves behind; a wave-BUILT terrace is the ramp of sediment laid down in deeper water at the seaward edge of that platform, out of the very debris the waves removed from the cliff

Sand bar→DEPOSITIONAL — a ridge of sediment thrown up by waves and longshore drift across a bay mouth or offshore. Longshore drift is the zig-zag transport produced when waves approach the beach obliquely and the backwash returns straight down the slope

Lagoon→DEPOSITIONAL — the sheet of shallow water impounded behind a bar, a spit or a reef. It exists only because sediment has been deposited across the entrance to a bay, and no amount of wave erosion produces one. It is the single item on which the near-miss choice in this question fails

Erosion and deposition work along the same stretch of coast at the same time, which is what makes this topic confusing and examinable: wave energy converges on the headlands and spreads out in the bays, so the headlands take the continuing attack while the quieter bays become places where deposition can begin. Hold each landform with a one-word tag for its process, and read every item in a list-type choice to the end — an examiner separating the careful candidate from the quick one builds the near-miss by changing exactly one item in the correct list. Indian coastal lagoons worth carrying: Chilika in Odisha, Pulicat between Andhra Pradesh and Tamil Nadu, and the Vembanad backwater in Kerala.

Study next

Depositional coastal landforms — beach, berm, spit, bar, tombolo, barrier island, lagoon and coastal dunes, with the mechanism of longshore driftEmergent and submergent coasts, the classification of the Indian coastline, and the ria, fjord and dalmatian coast typesCoral reefs and atolls — fringing, barrier and atoll forms, and Darwin's subsidence theoryMarine erosion processes in detail — hydraulic action, abrasion, attrition and solution — and how they vary with rock type and wave energyThe coast of Maharashtra and the Konkan — its physiography, creeks, ports and the Western Ghats escarpment behind it

Common traps

Grouping landforms by where they occur rather than by the process that made them; every item in every choice here is coastal, so location decides nothing
Confusing the wave-cut terrace, which is erosional, with the wave-built terrace, which is depositional, when the names differ by one word
Treating a lagoon as an erosional hollow when it is water impounded behind a bar or spit and therefore a product of deposition
Stopping after the first two items of a list-type option, when the near-miss choice differs from the correct one by exactly one entry

Coastal geomorphology reaches MPSC papers most often as a sorting question — which of these are erosional, which are depositional, which are found on an emergent coast — and occasionally as a sequence question asking for the order in which cave, arch, stack and stump appear. The commission also joins the physical process to Indian examples, so a question may name Chilika or the Malabar coast and ask what kind of feature it is. The efficient preparation is a single two-column table of erosional against depositional forms, learnt to the point where any name can be assigned without hesitation, plus a short list of named Indian instances for each. Once that table is secure, this whole family of questions becomes mechanical.

Related PYQs

No directly related past PYQ was found.

Practice

practice — not a real PYQ
Which one of the following coastal landforms is depositional rather than erosional in origin ?
- (a)Sea arch
- (b)Wave-cut platform
- (c)Tombolo
- (d)Sea stack
Answer(c) Tombolo — a ridge of sand or shingle deposited by waves and longshore drift that ties an offshore island to the mainland, and therefore a landform built out of transported sediment. The sea arch, the wave-cut platform and the sea stack are all products of marine erosion, the arch and the stack belonging to the same sequence of headland destruction that runs cave, arch, stack, stump.
practice — not a real PYQ
The progressive destruction of a rocky headland by wave erosion produces its landforms in which sequence ?
- (a)Stack, arch, cave, stump
- (b)Cave, arch, stack, stump
- (c)Arch, cave, stump, stack
- (d)Cave, stack, arch, stump
Answer(b) Cave, arch, stack, stump — waves first hollow out caves along joints on either side of the headland, the caves meet to leave an arch, the arch roof collapses and leaves the seaward mass standing alone as a stack, and continued attack cuts the stack down to a stump that is awash at high tide.