CDS (II) 2022 General Knowledge · Question 89 of 120

Correct — B, Peri-glacial. A pingo is a mound of earth-covered ice that grows in permafrost country in the Arctic and subarctic — ground that stays frozen year after year, near a glacier's world but not made by moving ice. That is what periglacial means, and it is the distinction the question is built on. Two kinds are recognised. A hydrostatic or closed-system pingo forms where a body of water is trapped as permafrost closes in around it and is squeezed upward as the water freezes and expands. A hydraulic or open-system pingo forms where groundwater under artesian pressure is forced up towards the surface and freezes there, usually at the foot of a slope. They rise from about 3 to 70 metres and span 30 to 1,000 metres across, and more than 11,000 are known worldwide — some 1,350 on the Tuktoyaktuk Peninsula in Canada and more than 1,500 in Alaska.

• (a)Glacial — Glacial landforms need a moving mass of ice to cut or to dump material — cirques, aretes and horns where ice erodes, moraines, drumlins and eskers where it deposits. A pingo has no glacier involved at all; its ice grows in place inside frozen ground.
• (c)Aeolian — Wind builds barchans and other dunes and carves yardangs and mushroom rocks, and it works best where the ground is dry and loose. Permafrost, which is what a pingo is made in, is the opposite condition.
• (d)Fluvial — Running water gives gorges and canyons, meanders and braided channels, plunge pools and floodplains. Water is certainly involved in a pingo, but as groundwater that freezes rather than as a stream that erodes and deposits.

Geomorphology sorts landforms by the agent that made them, and the periglacial set is easy to overlook because it sits between the glacial and the everyday. Periglacial processes work on ground that freezes and thaws and on permafrost that never fully thaws — frost heaving, ice wedges that crack the ground into polygons, solifluction where a thawed surface layer creeps over frozen ground below, patterned stone circles and stripes, and pingos. None of these needs a glacier.

Approach any landform-to-process item by asking what had to be present for the feature to exist. A pingo requires permanently frozen ground and water under pressure, and neither a glacier nor a river nor wind is needed, which leaves periglacial as the only category that fits. The pattern is worth practising because it recurs constantly in these papers: a cirque or an esker implies moving ice, a barchan implies wind, a plunge pool implies falling water, and lapies implies limestone dissolving underground.

• A pingo is an ice-cored mound covered by earth, formed in permafrost regions of the Arctic and subarctic.
• Periglacial means cold-climate processes near but not of a glacier; no moving ice is involved.
• A closed-system or hydrostatic pingo grows from water trapped by advancing permafrost and squeezed upward.
• An open-system or hydraulic pingo grows where artesian groundwater is forced up and freezes.
• Pingos stand 3 to 70 metres high and 30 to 1,000 metres across; over 11,000 are known, including about 1,350 on Canada's Tuktoyaktuk Peninsula.

• Reading peri-glacial as a synonym for glacial; the prefix means beside, not made by ice.
• Assigning any ice-related landform to a glacier.
• Treating a pingo as a volcanic or tectonic mound because of its dome shape.

As a landform-to-process item like this one, or as a match-the-list question pairing geomorphic agents with the features they produce.

• practice — not a real PYQ

  Which one of the following is a periglacial landform?

  • (a)Cirque
  • (b)Pingo
  • (c)Barchan
  • (d)Oxbow lake

  Answer(b) Pingo — an ice-cored mound formed in permafrost. A cirque is glacial, a barchan aeolian and an oxbow lake fluvial.

• practice — not a real PYQ

  Solifluction, the slow downslope creep of a thawed surface layer over frozen ground, belongs to which group of processes?

  • (a)Aeolian
  • (b)Periglacial
  • (c)Karst
  • (d)Coastal

  Answer(b) Periglacial — it needs a seasonally thawing active layer above permanently frozen ground.