Frost action and plucking are two key processes that contribute to glacial erosion by breaking down rocks and transporting the debris away, respectively.

Frost Action

Frost action, commonly referred to as freeze-thaw weathering, plays a significant role in glacial erosion. This process occurs when water infiltrates the cracks and crevices of rocks, where it subsequently freezes and expands. When water freezes, its volume increases by approximately $9\%$. This expansion generates considerable pressure on the surrounding rock, leading to cracking and fragmentation. Over time, repeated cycles of freezing and thawing result in substantial rock disintegration, a phenomenon known as frost shattering. This process is particularly effective in glacial environments, where temperatures frequently fluctuate around the freezing point.

Plucking

In contrast, plucking is the mechanism by which glaciers remove and transport these fragmented rocks. As a glacier advances over fractured rock, it can freeze onto the substrate. This occurs due to the pressure exerted by the overlying ice, which lowers the freezing point of water at the interface between the ice and the rock. This allows liquid water to exist and subsequently freeze onto the glacier. As the glacier moves, it ‘plucks’ these frozen rocks from the ground, incorporating them into the ice. Over time, these plucked rocks can be transported over considerable distances from their original locations.

Interconnection of Processes

Both frost action and plucking are essential to the glacial erosion process. Frost action generates the raw material by breaking down the rock, while plucking physically removes and transports this debris. Together, these processes reshape the landscape by eroding the underlying rock and redistributing the eroded material elsewhere. This can lead to the formation of distinctive glacial landforms, such as U-shaped valleys, cirques, and moraines.

Understanding these processes is crucial for geologists and environmental scientists who study the impacts of glaciers on the Earth’s surface.