Examkin

Question

Difficulty: MediumLandform Development by Wind Action and Glaciation

A field geologist observes a glaciated bedrock feature characterized by a smooth, gently inclined side facing the direction of ice advance and a steep, jagged slope on the down-flow side. Which landform and primary evolutionary process are described?

  1. Roche moutonnée formed by glacial abrasion and pluckingAnswer
  2. B
    Drumlin formed by subglacial till deposition
  3. C
    River terrace formed by rejuvenation and stream incision
  4. D
    Rock pedestal formed by differential in-situ weathering

Answer

Roche moutonnée formed by glacial abrasion and plucking
The correct answer identifies a roche moutonnée, an asymmetrical bedrock hill formed by glacial erosion. As moving glacial ice encounters a resistant rock obstacle, friction and debris at the glacier base abrade and smooth the up-ice (stoss) slope. On the down-ice (lee) slope, pressure release and refreezing of meltwater cause the ice to pluck out loose jointed rock blocks, leaving a steep, jagged cliff.

Step-by-Step Solution

1
Analyze the landform profile relative to ice movement direction.
The feature exhibits an asymmetrical slope with a smooth up-ice (stoss) side and a craggy down-ice (lee) side.
Slope asymmetry and orientation relative to ice flow are critical diagnostic criteria for glacial landforms.
2
Identify the erosional mechanisms responsible for the profile.
Abrasion smooths the stoss slope under heavy basal ice pressure, while plucking pulls away fractured bedrock on the lee side where pressure is reduced.
The combination of glacial abrasion and plucking acting on solid bedrock uniquely creates a roche moutonnée.
3
Distinguish this feature from depositional glacial and non-glacial landforms.
A drumlin has an inverted profile (steep stoss, gentle lee tail) and consists of deposited till rather than eroded bedrock, while terraces and pedestals originate from fluvial or aeolian/weathering action.
Eliminating options based on material composition and process origins confirms the correct choice.

Key Concept

Roche Moutonnée Formation and Glacial Erosional Processes
Rate this question

Topics

Landform Development by Wind Action and Glaciation

More questions from this topic