CDS (II) 2023 General Knowledge · Question 25 of 120

Correct — C, Zeugen. Of the three landforms named, only the zeugen is cut by wind. In an arid region where a resistant bed lies flat over a softer one, wind-driven sand travels close to the ground and grinds away at the weaker layer first; the hard cap is left standing on a narrowing pedestal, and a tabular ridge or mushroom-like mass results. That is abrasion — the sandblasting of rock by wind-borne grains — working together with deflation, the removal of loose fine material by wind turbulence. The other two options belong to entirely different agents. A cirque is an amphitheatre-like valley head formed by glacial erosion, the hollow in which a valley glacier is born; a tarn fills it, an arête separates two of them, and a horn stands where three or more meet. A stack is a steep, isolated column of rock standing in the sea near a coast, cut by wave erosion — waves widen a joint in a headland into a cave, the cave breaks through into an arch, and when the arch collapses the pillar left behind is the stack. Option D fails because it pairs the correct zeugen with that marine form.

• (a)Cirque — A glacial form, not an aeolian one. Ice, not wind, quarries and abrades the bowl-shaped hollow at the head of a glaciated valley, and cirques are found in high mountains and formerly glaciated uplands rather than in deserts.
• (b)Stack — A sea stack is carved by waves along a coast, through the cave-to-arch-to-stack-to-stump sequence. The word 'stack' tempts students who picture a heap of rock in a desert, but the landform is unambiguously marine.
• (d)Stack and Zeugen both — Half right, and therefore wrong. The zeugen belongs in the answer; the stack does not, because waves and not wind cut it.

Landforms are classified first by the agent that made them — running water, moving ice, waves, groundwater or wind. Wind works in two ways: deflation, the lifting and removal of loose fine-grained particles by turbulent air, and abrasion, the grinding of exposed rock by the sand the wind carries. Because wind-blown sand travels near the ground, abrasion bites hardest in the lowest metre or two, which is why undercut pedestals, mushroom rocks and yardang ridges are desert signatures. The zeugen belongs to this family.

The item is a one-word agent test dressed up as a landform question, and the fastest route to the answer is to place each name with its agent rather than to define it. Cirque goes with ice, stack goes with waves, and whatever is left must be the wind's. One honest caveat is worth carrying: 'zeugen' is the vocabulary of Indian and older British physical-geography texts, and the general encyclopedias carry no separate entry for it — the closest sourced definition is the yardang, 'a streamlined protuberance carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion by dust and sand and deflation'. The classical distinction taught in the texts is structural: a zeugen forms where a hard bed lies flat above a soft one, so the cap survives as a flat slab on a stalk, while yardangs form where the beds stand nearly on edge and are streamlined into long parallel ridges. Learn zeugen as the exam's own word for a wind-abrasion form; do not try to defend a precise metre-by-metre definition you cannot source.

• Wind erodes by deflation — 'the removal of loose, fine-grained particles by the turbulent action of the wind' — and by abrasion, 'the wearing down of surfaces by the grinding action and sandblasting by windborne particles'.
• A yardang is 'a streamlined protuberance carved from bedrock ... by the dual action of wind abrasion by dust and sand and deflation'; it forms where 'harder or less erodible material embedded in softer material' is exposed to strong, one-directional winds.
• A cirque is 'an amphitheatre-like valley formed by glacial erosion'; a tarn is the lake left on its floor, an arête the ridge between two cirques, and a horn — the Matterhorn is the standard example — the peak where three or more meet.
• A sea stack is 'a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion', the survivor of the crack, cave, arch, stack and stump sequence.
• Deserts also carry water-made forms — alluvial fans, bajadas, playas and pediments — so a landform being desert-located is not evidence that wind made it.

• Reading 'stack' as a desert pile of rock. It is a sea stack, and waves cut it.
• Assuming everything in a desert is wind-made — alluvial fans, bajadas and playas in the same deserts are water forms.
• Picking the 'both' option because two of the three names sound unfamiliar; in this item that option is exactly one landform too generous.

Usually as a one-liner asking which agent — wind, ice, running water or waves — produced a named landform, or as a match-the-landform-to-its-agent list.

• practice — not a real PYQ

  Which one of the following landforms is produced by glacial erosion?

  • (a)Barchan
  • (b)Cirque
  • (c)Stack
  • (d)Yardang

  Answer(b) Cirque — an amphitheatre-like hollow cut by ice at the head of a glaciated valley. A barchan and a yardang are wind forms and a stack is cut by waves.

• practice — not a real PYQ

  The sequence cave, arch, stack and stump describes landforms produced mainly by which one of the following agents?

  • (a)Wind
  • (b)Running water
  • (c)Sea waves
  • (d)Moving ice

  Answer(c) Sea waves — waves widen a joint in a headland into a cave, break the cave through into an arch, and leave a stack when the arch falls; the stack is later reduced to a stump.