How do abrasion and plucking reshape landscapes beneath glaciers?

Glaciers reshape landscapes through two primary erosional processes: abrasion and plucking. These mechanisms work together to carve, polish, and deepen the terrain beneath the ice.12

Abrasion

Abrasion occurs as a glacier slides over its bed, acting much like a sheet of sandpaper. Because ice is relatively soft, it relies on the rock debris embedded in its basal zone to perform the work of erosion. As the glacier moves, these hard rock fragments—ranging from fine particles to large boulders—grind against the underlying bedrock. This process creates various "tool-marks," such as microscopic scratches and deep gouges, and can erode the substrate by several tens of metres over thousands of years, resulting in streamlined landforms.12

Plucking

Plucking, or quarrying, involves the removal of larger, intact pieces of rock from the glacier bed. This process is driven by several factors:12
* Stress Gradients: As ice flows around bedrock obstacles, it creates differential stresses that can pull rock apart along existing joints or crack systems.1
* Regelation: Water beneath the glacier may refreeze in cavities, forcing rocks apart through the pressure of crystallization.1
* Hydraulic Pressure: The presence of subglacial water can exert hydraulic pressure that helps dislodge rock blocks.1

Once plucked, these larger rocks are incorporated into the glacier, where they serve as additional abrasive tools for further erosion. Together, these processes are responsible for creating distinct features such as U-shaped valleys, cirques, and fjords.134