Glaciers carve rock primarily through two processes: abrasion and plucking.
Abrasion: The Grinding Action
As a glacier moves downslope, the ice carries a vast amount of rock, sediment, and debris embedded within it. This material acts like sandpaper, grinding against the bedrock below. This process, called abrasion, creates distinctive scratches called striations on the rock surface. The size and depth of these striations indicate the intensity of the glacial erosion. Think of it like a giant, slow-moving sandblaster.
- Example: The presence of many deep striations on a rock face suggests a period of intense glacial activity with significant rock debris embedded in the ice.
Plucking: Lifting and Removing Rock
In addition to abrasion, glaciers also carve rock through a process called plucking. As the glacier moves, it melts at its base. This meltwater seeps into cracks and fissures in the bedrock. When the water refreezes, it expands, wedging pieces of rock loose. These loosened rock fragments then become embedded in the glacial ice and are transported away, leaving behind a jagged, uneven surface.
- Example: The presence of large, angular boulders far from their source location is indicative of glacial plucking and transportation.
The combined effects of abrasion and plucking significantly alter the landscape, creating U-shaped valleys, fjords, and other characteristic glacial landforms. The reference material supports this, stating: "As a glacier flows downslope, it drags the rock, sediment, and debris in its basal ice over the bedrock beneath it, grinding it. This process is known as abrasion and produces scratches (striations) in bedrock surface."
