CDS (II) 2024 General Knowledge · Question 77 of 120

Correct — D, Slow speed with soil. Mass movements are graded by how fast the material travels and how much water it carries. At the fast end are the landslides — slumps, debris slides, debris falls, rockslides and rock falls, all of them perceptible and involving relatively dry material. At the slow end sits creep, and its usual name in the literature is soil creep, defined as the slow downward progression of soil and weathered debris on a gentle slope under gravity. It is too slow to watch. You infer it from its effects: fence posts and telegraph poles leaning downhill, tree trunks curved at the base, terracettes stepping across a hillside, walls bulging outward. The mechanism is repeated small displacements — clay swelling when wet and shrinking as it dries, ground heaving as water freezes and settling again as it thaws — each cycle moving the particle a fraction downslope.

• (a)Fast speed with soil — Right material, wrong rate. Fast movements of soil and debris are earthflows, mudflows and debris slides, all of which are visible while they happen; creep is defined by being imperceptible.
• (b)Slow speed with rock — The tempting one, because rock creep and talus creep are real named variants. But the process is described and named for what it usually acts on, which is the soil and regolith mantle over a slope.
• (c)Slow speed with ice — Slow movement of ice is glacier flow, and slow movement of water-saturated soil over frozen ground is solifluction — related to creep but a separate named process of cold climates.

Mass movement is the transfer of slope material downhill under gravity alone, with no geomorphic agent such as running water, wind or ice doing the carrying. NCERT's chapter on geomorphic processes is careful about that distinction: because no agent transports the material, mass movement is not counted as erosion, even though material shifts. Weathering is not a precondition, but weathered slopes move far more readily than fresh rock. The three forms of movement are heave, flow and slide, and the whole family can be laid out on two axes — rate of movement and moisture content — with creep at the slow, drier end and mudflow at the fast, wet end.

Read the option as a pair of variables and the answer follows. Rate first: creep is by definition the imperceptible end of the spectrum, which kills any fast option. Material second: the word that travels with creep in every textbook is soil. The distractor built on rock exists because talus creep and rock creep are genuine terms, and the one built on ice exists because solifluction — a slow flow of water-saturated soil in cold regions, over ground that is frozen beneath — sits next to creep on the same chart. Keep the trio separate: creep for the soil mantle, solifluction for cold and saturated ground, glacier flow for ice.

• Mass movements are aided by gravity alone; no geomorphic agent such as running water, glaciers, wind or waves takes part, which is why they are not classed as erosion.
• The three forms of movement are heave, flow and slide, and the family is arranged by rate of movement against moisture content.
• Landslides — slump, debris slide, debris fall, rockslide and rock fall — are the rapid, perceptible movements, involving relatively dry material.
• Creep is the slow downward progression of soil and weathered debris on gentle slopes, driven by repeated swelling and shrinking or freezing and thawing.
• Solifluction is the slow downslope flow of water-saturated soil in cold climates, and is a separate named process from ordinary soil creep.

• Reading creep as any slow process, and so attaching it to ice or to bedrock.
• Counting mass movement as a form of erosion; no transporting agent is involved.
• Confusing solifluction with ordinary soil creep — the saturated, cold-climate case has its own name.

By naming a process and asking for its rate and material, or by giving a field observation such as tilted poles and asking which process produced it.

• practice — not a real PYQ

  Leaning fence posts, curved tree trunks and small terraced steps on a grassy hillside are the usual field evidence for which process?

  • (a)Soil creep
  • (b)Rock fall
  • (c)Sheet erosion
  • (d)Solifluction

  Answer(a) Soil creep — the movement is too slow to see, so it is read from the objects it slowly tilts.

• practice — not a real PYQ

  Which of the following is a rapid mass movement?

  • (a)Creep
  • (b)Solifluction
  • (c)Rockslide
  • (d)Talus creep

  Answer(c) Rockslide — the sliding of rock masses along bedding, joint or fault surfaces, which on steep slopes is very fast and destructive.