MPSC 2021 Prelims Paper-I · Question 21 of 100

Correct — option (3), which reads (a) - (iv), (b) - (i), (c) - (ii), (d) - (iii). Plateaus in this classification are named for how they were made, not for where they are, so each item in the first column is a mode of origin and the second column has to be read for the origin each example records. Three of the four pairs can be settled independently, and once they are settled the fourth is forced. Start with the Lava Plateau at (c). The Columbia Plateau — printed here as 'Colombia Plateau' — lies between the Cascade Range and the Rocky Mountains in Washington, Oregon and Idaho and is a flood-basalt plateau: successive fissure eruptions of the Columbia River Basalt Group in the late Miocene and early Pliocene piled lava to more than 1.8 km in places over some 63,000 square miles, drowning the older relief and leaving a broad, slightly sagging basalt surface. Nothing else in the second column was built by lava, so (c) takes (ii). Next the Glacier Erosion Plateau at (d). Greenland is the only entry that carries an ice sheet, and an ice-scoured plateau is by definition the work of moving ice, so (d) takes (iii). Then the Intermont Plateau at (a) — a plateau enclosed within or shut in by mountain ranges. Balochistan, printed 'Baluchisthan', is described as an extensive plateau of rough terrain divided into basins by ranges of significant height and ruggedness, sitting on the south-eastern edge of the Iranian plateau; that is exactly the intermontane setting, so (a) takes (iv). Three slots in the second column are now spent, and only the Colorado Plateau at (i) is left, so the Piedmont Plateau at (b) must take it — a piedmont plateau being one that lies at the foot of a mountain range, and the Colorado Plateau does lie against the flank of the Rocky Mountains on its eastern and northern sides. That completes (a) - (iv), (b) - (i), (c) - (ii), (d) - (iii), which is option (3).

• (1)(a) - (i), (b) - (ii), (c) - (iii), (d) - (iv) — This row pairs the Lava Plateau with Greenland and the Glacier Erosion Plateau with Balochistan, and both are impossible. Greenland's plateau surface is the product of ice, not of fissure eruptions; there is no flood-basalt province beneath the ice sheet that gives the island its plateau form, and the item is in the list precisely because it is the ice example. Balochistan, at the other end, is a dry sub-tropical plateau on the edge of the Iranian plateau with no ice sheet and no record of Pleistocene ice-sheet scouring of the kind that shapes a glacier-erosion plateau. The row also gives the Intermont Plateau to Colorado, which is the one pair a candidate might argue for, and that is what makes the row attractive; but the two impossible pairs at (c) and (d) kill it before that argument is worth having.
• (2)(a) - (iii), (b) - (ii), (c) - (i), (d) - (iv) — Here the Intermont Plateau is given to Greenland and the Glacier Erosion Plateau to Balochistan, so the row inverts the single most obvious pair in the question. Greenland is not shut in by mountain ranges — its plateau is an ice sheet resting in a bedrock basin rimmed by coastal highlands, and it is in this list as the ice example. Balochistan carries no ice. The row further hands the Lava Plateau to Colorado, whose surface is a thick, largely undeformed pile of sedimentary rock — sandstone, shale and limestone into which the Colorado river has cut the Grand Canyon — not a basalt sheet. The habit that disposes of this row in seconds is to find the one example that can belong to only one category, which here is Greenland, and to strike out every row that spends it elsewhere.
• (4)(a) - (iv), (b) - (ii), (c) - (i), (d) - (iii) — This is the near-miss, and it is the row worth studying. It gets the two anchors right — Intermont with Balochistan and Glacier Erosion with Greenland — and then swaps the remaining two, giving the Piedmont Plateau to Columbia and the Lava Plateau to Colorado. That swap is the error. The Columbia Plateau is the textbook flood-basalt plateau of North America, built by the Columbia River Basalt Group, while the Colorado Plateau is a thick, stable block of layered sedimentary rock that was uplifted rather than erupted. A candidate who verifies only the pairs that are easy will accept this row, which is precisely how it is built: a setter who leaves the easy pairs intact has done so deliberately. In a paper that deducts a quarter of a question's marks for a wrong answer, checking the last two pairs is worth the few seconds it costs.

Plateaus are elevated tablelands with a comparatively level top and at least one steep side, and geography classifies them by how they came to be. An intermontane plateau is enclosed by, or lies between, mountain ranges — Tibet between the Himalaya and the Kunlun is the largest, and the Bolivian altiplano and Balochistan belong to the same family; these are usually the highest and most extensive plateaus because they were lifted with the ranges that hem them in. A piedmont plateau lies at the foot of a mountain range, with a plain or a sea on its other flank, the name coming from the Latin for foot and mountain. A continental or tableland plateau rises abruptly from a lowland or a coast, as the Deccan and the Chota Nagpur plateaus do. A lava or volcanic plateau is built up rather than uplifted: fissure eruptions of low-viscosity basalt spread in sheet after sheet until the older relief is buried, which is how the Columbia Plateau in the United States and the Deccan Traps in India were made. A glacier-erosion plateau is a surface planed and scoured by an ice sheet, of which Greenland and Antarctica are the standard examples. Two further terms are worth carrying: a dissected plateau is one that streams have cut into a maze of valleys and residual flat tops, and a continental shield is an ancient plateau of crystalline rock worn low over geological time.

MPSC's physical geography block leans on the four-by-four match because it can test four definitions in the space of one question, and this one is built on the classification of plateaus by origin. The technique it rewards is not recall of a list but the ability to see which cell in the second column can belong to only one category. Greenland can only be the ice example; Columbia can only be the lava example; those two decide the question, and the rest follows by elimination. Working through the pairs in printed order, by contrast, invites a candidate to stall on the pair they are least sure of and then guess the whole row. The second thing this question teaches is that the two columns are printed side by side because the reader has to match them — the adjacency of Intermont Plateau and Colorado Plateau on the page asserts nothing at all. That is worth repeating because the layout of every matching question in this paper tempts the eye into reading a pairing off the printed rows.

• An intermontane plateau is enclosed by or lies between mountain ranges; Tibet, the Bolivian altiplano and Balochistan are the standard examples, and such plateaus are generally the world's highest because they rose with the ranges around them.
• A piedmont plateau lies at the foot of a mountain range with a plain or sea beyond it — the name is from the Latin for foot and mountain — while a continental or tableland plateau rises straight from a lowland, as the Deccan does.
• The Columbia Plateau in Washington, Oregon and Idaho is a flood-basalt plateau of the Columbia River Basalt Group: late Miocene to early Pliocene fissure eruptions laid lava more than 1.8 km thick over roughly 63,000 square miles.
• The Colorado Plateau covers about 340,000 sq km around the Four Corners of the United States at 1,500 to 3,350 m, is bounded by the Rocky Mountains on its east and north, and is a thick block of layered sedimentary rock into which the Grand Canyon is cut.
• Greenland and Antarctica are the textbook glacier-erosion plateaus, their surfaces being ice sheets over bedrock that continental ice has scoured; the Deccan Traps are India's own lava plateau.

• Reading a pairing off the printed layout because the two lists sit side by side — the adjacency is typesetting, and a matching question asserts no pair until you make it
• Confusing the Columbia Plateau, a flood-basalt plateau of the Pacific Northwest, with the Colorado Plateau, a stable block of sedimentary rock around the Four Corners; the English column of this paper prints the first name in two different spellings on two different pages, 'Colombia Plateau' here and 'Columbia plateau' at Q26, while the Marathi column writes कोलंबिया in both
• Treating the classification of plateaus as fixed and universal — the same plateau is placed in different classes by different textbooks, so anchor a matching row on the examples that can belong to only one class and let the rest follow
• Verifying only the pairs you are sure of and accepting a row that swaps the two you are not, which is exactly how the near-miss row in this question is built

Plateau classification reaches MPSC papers in three shapes. The first is this four-by-four match of a plateau type against an example, which is the commonest. The second is a one-line item asking what a named plateau is, or which continent it belongs to — this very paper asks that separately a few questions later, and it prints the same Columbia plateau again. The third is an origin question: which of the following is a lava plateau, or which was formed by glacial erosion. A single page carrying the five origin classes, two world examples and one Indian example each, and a note of the plateaus that different books classify differently, covers all three shapes. Pair it with the world's major plateaus by continent, since the Commission likes to test the type and the location of the same plateau in adjacent questions.

No directly related past PYQ was found.

• practice — not a real PYQ

  The Columbia Plateau of the north-western United States, built by successive fissure eruptions of the Columbia River Basalt Group, is an example of which kind of plateau?

  • (a)an intermontane plateau
  • (b)a piedmont plateau
  • (c)a lava or volcanic plateau
  • (d)a plateau of glacial erosion

  Answer(c) a lava or volcanic plateau — it was built up by sheet after sheet of low-viscosity basalt erupted from fissures in the late Miocene and early Pliocene, in places more than 1.8 km thick over some 63,000 square miles, burying the older relief. An intermontane plateau such as Tibet or Balochistan is enclosed by mountain ranges, a piedmont plateau lies at the foot of one, and a glacial-erosion plateau such as Greenland is planed by an ice sheet.

• practice — not a real PYQ

  Which one of the following pairs of plateau and the continent it lies in is correctly matched?

  • (a)Massif Central — Asia
  • (b)Altiplano — Africa
  • (c)Yunnan plateau — Europe
  • (d)Colorado Plateau — North America

  Answer(d) Colorado Plateau — North America. It covers about 340,000 sq km around the Four Corners region of the United States, at 1,500 to 3,350 m, and the Grand Canyon is cut into it. The Massif Central is in France and therefore Europe, the Altiplano is the Bolivian plateau of South America, and the Yunnan plateau is in southern China and therefore Asia.