glacial processes and landforms

Answer: Freeze-thaw weathering occurs when water enters cracks and joints in rock during warmer conditions (1 mark). When temperatures drop below 0°C, the water freezes and expands by approximately 9%, exerting pressure on the rock (1 mark). Repeated freeze-thaw cycles gradually widen the cracks (1 mark). Eventually, angular rock fragments break off and accumulate as scree at the base of the slope (1 mark).

Answer: Freeze-thaw weathering occurs when water enters cracks and joints in rock during warmer conditions (1 mark). When temperatures drop below 0°C, the water freezes and expands by approximately 9%, exerting pressure on the rock (1 mark). Repeated freeze-thaw cycles gradually widen the cracks (1 mark). Eventually, angular rock fragments break off and accumulate as scree at the base of the slope (1 mark).

Answer: A corrie begins when snow accumulates in a sheltered hollow on the mountainside (1 mark). The snow compacts into firn and then glacial ice, and the growing glacier begins to erode through abrasion and plucking (1 mark). Rotational flow deepens the floor and steepens the back wall through freeze-thaw weathering and plucking (1 mark). When the glacier melts, the armchair-shaped hollow remains, often filled with a tarn (corrie lake) behind the raised lip of rock at the front (1 mark).

Answer: Abrasion occurs when debris frozen into the base of the glacier scrapes and grinds against the bedrock as the ice moves (1 mark), producing smooth, polished surfaces with parallel striations (1 mark). Plucking occurs when meltwater seeps into cracks in the bedrock, refreezes and attaches rock to the glacier, which then pulls fragments away as it moves (1 mark), producing jagged, angular surfaces on the downstream side of obstacles (1 mark). Abrasion is most effective when the glacier carries a large coarse load, while plucking is most effective where there are well-jointed rocks (1 mark). Both processes operate together - plucking loosens material that abrasion then uses to grind the bedrock (1 mark). They create different surface textures: smooth and striated for abrasion, rough and angular for plucking (1 mark).

Answer: I agree that deposition landforms are very important for understanding ice movements because moraines directly mark the position of the glacier at different times - terminal moraines show the maximum extent, and recessional moraines show pauses in retreat (1 mark). Erratics can be traced back to their source, revealing the direction of ice flow (1 mark). Drumlins are aligned in the direction of ice movement, showing the path of glaciers across the landscape (1 mark). However, erosion landforms also provide valuable information - corries indicate the presence and altitude of glaciers (1 mark). Arêtes and pyramidal peaks show where multiple glaciers converged (1 mark). U-shaped valleys and truncated spurs reveal the scale and power of the glacier (1 mark). Striations on bedrock show the precise direction of ice movement at that point (1 mark). Both types are complementary - erosion landforms show where ice was active and how powerful it was, while deposition landforms show where ice stopped and what it carried (1 mark). Together, they provide a more complete picture than either alone, but deposition landforms are arguably more useful for mapping ice extent and movement because they leave clearer, more datable evidence (1 mark).