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How do glaciers erode bedrock through abrasion and plucking?

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esker: Nunavut — glacial landform Eskers, or narrow ridges of gravel and sand left by a retreating glacier, wind through western Nunavut, Canada, near the Thelon River.

Glaciers erode bedrock primarily through two distinct processes: abrasion and plucking (also known as quarrying).12

Abrasion

Glacial abrasion functions similarly to sandpaper. Because ice is relatively soft, it cannot significantly erode solid bedrock on its own. Instead, it uses a basal debris zone—a layer of rock fragments ranging from fine particles to large boulders—that becomes embedded in the ice. As the glacier slides over its bed, these hard rock "tools" are dragged across the surface, grinding, scratching, and polishing the bedrock. This process creates various features, including microscopic scratches, deep gouges, and striations.134

Plucking

Plucking involves the removal of larger, intact pieces of rock from the glacier bed. This occurs through several mechanisms:1
* Stress and Fracturing: As ice flows around bedrock obstacles, high stress gradients and tensile forces can pull rock apart along existing joints or crack systems.1
* Regelation: Water beneath the glacier may refreeze in cavities, exerting pressure that forces rock fragments apart.1
* Hydraulic Pressure: The presence of subglacial meltwater can exert hydraulic pressure that helps dislodge rock.1

Once plucked, these larger fragments are incorporated into the glacier, where they often become additional "tools" for further abrasion.1