The processes of glacial erosion and deposition and the resulting upland landforms, and the processes of coastal erosion and deposition and the resulting features of erosion and deposition.

What this key area is asking

The SQA wants you to explain how moving ice and the sea erode, transport and deposit material, and to describe the upland glacial landforms and coastal landforms that result. You should anchor your answer in named Scottish landscapes such as the Cairngorms for glaciation and Orkney or the Ayrshire coast for coastal features. As always at Higher, marks come from linking a named process to a named, located landform.

Glacial processes

Two further processes prepare and transport material. Freeze-thaw weathering (frost shattering) above the ice supplies angular debris that falls onto the glacier, and bulldozing pushes loose material ahead of the ice. The eroded and weathered debris is carried within and beneath the ice until it melts out.

Glacial landforms

Erosional landforms. A corrie is an armchair hollow on a mountainside where snow accumulated and ice rotated, deepening the hollow by plucking the back wall and abrading the floor; a rock lip holds a small lake (a tarn) such as Lochan Coire an Lochain in the Cairngorms. Where two corries erode back to back they leave a sharp arete, and three or more leave a pyramidal peak. A glacier moving down a pre-existing river valley straightens and deepens it into a U-shaped valley (glacial trough), truncating the old interlocking spurs to leave truncated spurs and leaving tributary valleys high up as hanging valleys. The Lairig Ghru, a deep through-valley in the Cairngorms, is a textbook glacial trough.

Depositional landforms. As ice melts it drops unsorted angular debris called till (boulder clay). Moraine is till deposited as ridges: lateral moraine along the valley sides, medial moraine where two glaciers merge, terminal moraine at the snout, and ground moraine spread across the floor. Drumlins are smooth, egg-shaped mounds of till, with a steep stoss (up-ice) end and a tapering lee end, aligned with the direction of ice flow.

Coastal processes

Whether the coast erodes or builds depends on wave energy. Destructive waves (high, frequent, strong backwash) dominate erosion; constructive waves (low, less frequent, strong swash) dominate deposition and beach building.

Coastal landforms

Erosional landforms. Where bands of hard and soft rock meet the coast at an angle (a discordant coast), the soft rock is eroded back into bays and the hard rock stands out as headlands. Waves then attack lines of weakness in a headland to cut a cave, which is widened and driven through the headland into an arch; when the unsupported arch roof collapses it leaves an isolated stack (the Old Man of Hoy, Orkney, stands about $137\ m$ high), and the eroded stack is reduced to a stump. A retreating cliff leaves a gently sloping wave-cut platform at its base.

Depositional landforms. Where waves lose energy in sheltered water, sediment builds beaches. Where the coastline changes direction or a river mouth interrupts it, longshore drift extends sediment across the gap as a spit, whose end may curve landward (a recurved spit) under wave refraction or a secondary wind. A spit that grows right across a bay becomes a bar, trapping a lagoon behind it.

Examples in context

Example 1. The Cairngorms glacial landscape. The Cairngorms in the Scottish Highlands preserve a near-complete glacial toolkit from the last ice age, which ended around 11,500 years ago. North and east facing corries such as Coire an Lochain and Coire an t-Sneachda hold tarns behind rock lips; aretes separate adjacent corries; the Lairig Ghru is a deep U-shaped through-valley; and moraine ridges and till deposits mark where the ice melted. Using one named upland lets you describe both erosional and depositional landforms with located evidence.

Example 2. The Orkney coastline. Orkney shows classic coastal erosion in resistant Old Red Sandstone. The Old Man of Hoy, a sea stack about $137\ m$ tall, is the end product of the crack, cave, arch, stack sequence, and the surrounding cliffs and wave-cut platforms record continuing destructive-wave erosion. By contrast, sheltered bays on the same archipelago show depositional beaches, illustrating how wave energy and rock resistance together decide whether a stretch of coast erodes or builds.

Try this

Q1. Explain the formation of a corrie. [4 marks]

• Cue. Snow collects in a shaded hollow and compacts to ice; rotational movement and plucking steepen the back wall while abrasion deepens the floor; a rock lip holds a tarn once the ice melts.

Q2. Explain how a spit is formed. [4 marks]

• Cue. Longshore drift moves sediment along the coast; where the coastline changes direction the material is deposited across the gap and builds outwards; the prevailing wind or wave refraction may curve the end into a recurved spit.