Glacial Erosion – Detachment mechanism What is the term for the process by which moving glacial ice plucks, detaches, and removes blocks from bedrock, contributing to erosional shaping of valleys and cirques?

Introduction / Context:Glaciers reshape landscapes using two principal erosional mechanisms: abrasion and plucking (also called quarrying). Recognizing the distinct processes clarifies why glaciated bedrock shows both smoothed striated surfaces and jagged quarried faces.

Given Data / Assumptions:

• We need the name of the process that detaches and removes rock blocks.
• Moving glacial ice interacts with jointed or fractured bedrock.
• Only one option precisely describes this detachment mechanism.

Concept / Approach:Plucking occurs when meltwater infiltrates rock joints beneath a glacier, freezes, and bonds rock to the base of the ice. As the glacier advances, these frozen-in blocks are pried out and carried away. Abrasion is different: it grinds and polishes bedrock using rock fragments embedded in the basal ice, leaving striations and grooves. Scouring is a general term for erosive action but lacks the specific detachment mechanism implied here.

Step-by-Step Solution:Identify the key action: detachment of blocks from bedrock.Match mechanism: freeze-on and extraction → plucking (quarrying).Eliminate abrasion (grinding) and vague scouring.

Verification / Alternative check:Field evidence includes roche moutonnée forms with a smooth stoss side (abrasion) and a steep, plucked lee side (plucking), demonstrating the complementary roles.

Why Other Options Are Wrong:

• abrasion: polishing/striations rather than block detachment.
• scouring: non-specific; could include various erosive actions but not the precise freeze–thaw extraction.
• None of the above: incorrect because plucking is the established term.

Common Pitfalls:Assuming abrasion alone explains jagged lee faces; block removal is characteristic of plucking.

Final Answer:plucking