The correct option is 2 and 3 only.
Explanation
Glacial erosion is a powerful exogenic process driven by the movement of large ice masses. The two primary mechanisms of glacial erosion are plucking (quarrying) and abrasion. These processes allow glaciers to modify landscapes significantly, carving out distinctive landforms.
Statement 1 is Incorrect:
The statement describes the process of abrasion, not plucking. Plucking occurs when meltwater at the base of the glacier enters cracks and joints in the bedrock, freezes, and expands (frost wedging), thereby detaching blocks of rock which become embedded in the ice. The process described in the statement-dragging rock fragments along the floor to scour the bedrock-is the definition of abrasion.
Statement 2 is Correct:
Glaciers are capable of causing significant erosion to un-weathered rocks. Unlike wind or running water, which often require material to be loosened by weathering first, the sheer mass of a glacier and the rock debris embedded within it allow it to grind down and remove solid, fresh bedrock effectively.
Statement 3 is Correct:
The sheer weight of the overlying ice exerts immense pressure on the valley floor. This pressure creates friction between the basal ice (loaded with rock debris) and the bedrock. This friction is the driving force behind abrasion, acting like sandpaper to polish, scratch, and groove the rock surface.
Key Takeaway:
Plucking is the detachment of rock blocks via freeze-thaw action, while abrasion is the grinding and polishing of bedrock by debris dragged by the moving ice.