C.2 Physical processes and landscapes

Surface A is jagged and angular with blocks removed along existing weaknesses (joints). Surface B is smooth with parallel linear scratches. These are the diagnostic surface signatures of two distinct glacial erosion processes.

Plucking occurs when meltwater refreezes into rock joints, bonding the rock to the glacier. As ice moves forward, discrete blocks are torn away, leaving a rough, angular, block-removed surface. This matches Surface A exactly.

Abrasion occurs when debris already embedded in the glacier base is dragged across bedrock, acting like sandpaper. This produces polished, smooth surfaces with long parallel scratches called striations, which matches Surface B.

Surface A = plucking (angular, block-removal) and Surface B = abrasion (smooth, striated). The correct answer is: Surface A formed by plucking; Surface B formed by abrasion.

The question asks which pairing correctly links each surface description to its glacial erosion process. Two processes must be correctly assigned to two contrasting surfaces.

This reverses the correct pairing. Abrasion produces smooth, striated surfaces, not jagged block-removal surfaces, so assigning abrasion to Surface A is incorrect.

Meltwater erosion is not one of the two standard glacial erosion mechanisms (plucking and abrasion). Also, plucking produces angular surfaces, not smooth striated ones, so assigning plucking to Surface B is wrong.

Freeze-thaw weathering is a weathering process, not a glacial erosion process. Abrasion produces smooth surfaces, not jagged angular ones, so this pairing is doubly incorrect.

The only accurate pairing is Surface A formed by plucking (block removal, angular) and Surface B formed by abrasion (smooth, striated scratches).

The ridge is: (1) unsorted, angular till — indicating deposition directly from ice, not meltwater; (2) crossing the full valley width — not running parallel to the sides; (3) crescent-shaped, curving downvalley; (4) located 8 km beyond the current snout.

A terminal moraine crosses the full width of a valley floor in a crescent shape at the maximum historical extent of the glacier's snout. Unsorted till confirms direct ice deposition. The snout is now 8 km further upvalley because the glacier has since retreated.

Lateral moraines run parallel to valley sides; medial moraines run down the glacier's centre; recessional moraines also cross the valley but sit between the terminal moraine and the current snout, marking pauses during overall retreat — they are not the outermost ridge.

All characteristics point to a terminal moraine: full valley-width, crescent-shaped, unsorted till, outermost ridge position, indicating the glacier's maximum historical advance.

The question asks for the correct landform identification and its significance, given specific physical characteristics of an unsorted ridge crossing a valley.

A lateral moraine runs parallel to ice flow along valley sides, not across the full valley floor in a crescent. The ridge described crosses the entire valley width, ruling out a lateral moraine.

A medial moraine runs down the centre of a glacier, not across the valley floor as a crescent arc. It also forms from two merging lateral moraines, which is not described in the scenario.

A recessional moraine is also a cross-valley ridge, but it forms during a pause in retreat, not at the maximum extent. The fact that this is the outermost ridge, 8 km beyond the current snout, indicates maximum extent rather than a pause during overall retreat.

The only matching landform is a terminal moraine: a full-width, crescent-shaped, unsorted till ridge deposited when the glacier's snout stalled at its furthest point of advance.