Plucking (glaciation)

Plucking, also known as quarrying, is a glacial erosion process that contributes significantly to the shaping of landscapes in glaciated areas. It occurs when meltwater penetrates cracks and fissures in the bedrock beneath a glacier. As the water refreezes, it expands, exerting pressure on the surrounding rock. This process, freeze-thaw weathering, weakens the rock.

As the glacier moves forward, it incorporates the loosened rock fragments into its base and sides. The ice essentially "plucks" these pieces away from the bedrock. Plucking is particularly effective on the down-glacier side of a rocky outcrop or hill, leading to the formation of distinctive features such as roches moutonnées.

The size of the rock fragments removed by plucking can vary considerably, ranging from small pebbles to large boulders. These plucked rocks are then transported by the glacier and may eventually be deposited as glacial erratics far from their original source. The process is more effective on fractured and jointed rock, as these weaknesses provide pathways for meltwater to infiltrate. The rate of plucking depends on factors such as the temperature fluctuations around the freezing point of water, the presence of meltwater, the bedrock geology, and the velocity of the glacier.