Geomorphology Questions and Answers

Answer: D

The answer is (3) and (4): making ox-bow lakes and a floodplain.

In the mature stage a river's gradient is gentler, so it erodes sideways more than downwards. It swings in wide meanders, and when a meander loop is cut off an ox-bow lake is left behind. Lateral erosion and deposition during floods build a broad, flat floodplain.

Deepening the valley by vertical erosion, producing V-shaped valleys, gorges and waterfalls, is the work of the youthful stage. A delta forms at the river's mouth in the old stage, where the river deposits its load on entering a sea or lake. So options containing (1) or (2) are wrong.

Answer: A

The process is Freeze and Thaw.

Freeze-thaw weathering (frost wedging) happens when water in rock cracks freezes, expands by about 9 per cent and widens the crack, then thaws and refreezes again and again. It needs temperatures that swing above and below 0°C, so in the tropics it occurs only on high mountains, in alpine conditions.

The other processes are active in the tropics. Chelation is chemical weathering by organic compounds that bind metal ions, common under dense tropical vegetation. Granular disintegration from repeated heating and cooling of mineral grains is typical of hot deserts, and oxidation of iron-bearing minerals is widespread in warm, humid climates (it gives laterites their red colour).

Answer: C

The keyed match is a-3, b-4, c-2, d-1.

• Glaciers: a crevasse is a deep crack in a glacier's ice (a-3).
• Coasts: cusps (beach cusps) are regular crescent-shaped scallops along a beach (b-4).
• River: a chute is a channel a river cuts across the neck of a meander or a bar (c-2).
• That leaves castle kopjes for karst (d-1).

Strictly, castle kopjes are granite tors of the African savanna rather than karst forms, so the last pair is filled by elimination; the first three pairs are unambiguous and fit only this option. Options B and D place cusps with glaciers, and option A puts castle kopjes on the coast, so all break a pair that is certain.

Answer: A

The keyed answer is Hinosphere, the paper's spelling of the chionosphere.

The chionosphere is the layer of the atmosphere, and the zone of the Earth's surface, in which snow can persist through the year. Its lower boundary is the snow line. Above a certain height the air becomes too dry for further snow accumulation, which is the upper limit the stem refers to, so the snow line demarcates this zone.

A snow patch is a small, isolated patch of snow that survives into summer. A glacial trough is a U-shaped valley carved by a glacier, and a nunatak is a rock peak projecting above an ice sheet. None of them is the zone bounded by the snow line.

Answer: B

The correct pairs are (1), (3) and (4).

Granite is the typical rock of batholiths, the huge intrusive bodies formed when magma cools deep underground (1). Quartzite is extremely resistant and so stands out as ridge crests (3). Hard, resistant rocks survive as monadnocks, isolated hills rising above a peneplain (4).

Pair (2) is wrong. Hogback ridges are formed by steeply dipping beds of resistant sedimentary rock such as sandstone, alternating with weaker beds. Marble is a metamorphosed limestone that dissolves readily and does not form hogbacks. So every option containing (2) fails.

Answer: A

The correct match is a-3, b-1, c-4, d-2.

• Simultaneous uplift and erosion: W. Penck, whose model (1924) related slope form to the rate of uplift relative to erosion (a-3).
• Erosion of a stable landmass: W.M. Davis, whose cycle of erosion assumes rapid uplift followed by a long period of stability (b-1).
• Morphometric analysis: A.N. Strahler, who put drainage basins on a quantitative footing with stream ordering (c-4).
• Pediplanation in semi-arid regions: L.C. King, who explained landscapes by the parallel retreat of slopes and the spread of pediments (d-2).

Option B confuses King with Penck, and options C and D misplace Davis or Strahler.

Answer: A

The key is Both (A) and (R) are true and (R) is the correct explanation of (A).

Headward (backward) erosion is the cutting back of a stream at its source, so the stream is lengthened up its own valley. When this lengthening carries the head of one stream through the divide into the valley of a neighbour, the neighbour's upper course is diverted into the more actively eroding stream. That is river capture, or piracy, so (A) is true. (R) is true too: the elongation of a stream in its source region is what headward erosion does.

The weak point is (R). Elongation at the source is nearly the definition of headward erosion rather than a separate cause, so a reader could call (R) a restatement and prefer 'true but not the explanation'. No source found settles that choice, so the answer follows the key: the lengthening at the source is the mechanism that brings a stream to the divide and into position to capture another. Options C and D are wrong because neither statement is false.

Answer: D

The key is an autochthonous zone, and this is the key's reading rather than a settled fact.

Structural geologists divide the Himalaya by thrusts into the Siwalik, Lesser Himalaya, Great (Higher) Himalaya and Tethys zones. Rocks lying roughly where they formed are called autochthonous, rocks moved a short way para-autochthonous, and rocks carried far over others allochthonous. No source found labels the Great Himalaya autochthonous; descriptions of the Main Central Thrust speak of high-grade Greater Himalayan rocks lying over the lower-grade Lesser Himalayan rocks, which points the other way.

A suture zone is certainly wrong: the Indus-Tsangpo suture lies north of the Great Himalaya, where the Indian and Eurasian plates joined. The para-autochthonous label is the one usually attached to the Lesser Himalaya, in the south. Of the options, the key treats the Great Himalaya as the autochthonous core, so choose D.

Answer: C

Embankments built parallel to a river for flood protection are Levees.

Artificial levees (embankments or bunds) run along the banks to confine floodwater to the channel, as along the Kosi, Brahmaputra and Mississippi. Natural levees form the same way when floodwater drops sediment next to the channel.

Groynes are built across or at an angle to the flow to deflect water and protect banks or beaches, guide banks steer a river through a bridge opening, and terraces are old floodplain levels left by river incision, not flood defences.

Answer: A

Only statement i is correct, so the answer is (i) only.

A barchan is a crescent-shaped dune formed where the wind blows from one direction over a limited supply of sand. Its horns (the points of the crescent) extend downwind, because sand moves faster around the thinner edges (i).

Statement ii is wrong: the upwind (stoss) side is the gentle slope up which sand is blown. Statement iii is wrong: the downwind side inside the crescent is the steep slip face, standing near the angle of repose of about 32-34°. So any option including ii or iii fails.