Reading: Matching Features: Question 9

Four Shapes the Sea Carves into the Land

Where land meets ocean, the resulting coastline can take strikingly different forms depending on the geological processes that shaped it long before the sea reached its present level. Four coastal landforms in particular are often confused with one another, because each involves water intruding into what was once dry land, even though the processes that created them, and the shapes that result, are quite distinct.

Fjords begin as steep-sided valleys gouged out by glaciers during past ice ages, when moving ice carved a deep, U-shaped trough far below current sea level. When the ice retreated and global sea levels rose, the ocean flooded these troughs, producing long, narrow inlets with near-vertical rock walls and water that can exceed several hundred metres in depth close to shore. A shallow underwater ridge, or sill, often marks the point where the ancient glacier once ended.

Rias form through a different process entirely: rising sea levels drowning the lower reaches of an ordinary river valley that was never touched by glacial ice. Because the valley was originally carved by a river rather than a glacier, a ria has a V-shaped cross-section rather than a fjord's U-shape, its depth decreases gradually toward the river mouth, and it typically lacks the deep underwater sill found at a fjord's entrance.

Barrier islands are elongated ridges of sand built up parallel to the mainland shore by the combined action of waves, tides and longshore currents depositing sediment offshore. A shallow, sheltered lagoon typically separates the island from the mainland, and because the islands are made of loose sand rather than solid rock, storms can shift their shape dramatically within a single season, sometimes opening a new inlet or closing an old one entirely.

Mangrove coasts develop where fine river-borne sediment accumulates along low-energy, sheltered tropical shorelines, creating soft mudflats that salt-tolerant mangrove trees are able to colonise. The dense root systems anchoring these trees trap yet more sediment with each tide, while providing a nursery habitat for young fish and crustaceans that shelter among the submerged roots at high tide.

Sea cliffs, by contrast, form where waves attack an exposed, resistant rockface directly, undercutting its base until the unsupported rock above collapses; the coastline then retreats gradually inland over centuries rather than advancing seaward, and unlike the four landforms above, no flooding or sediment deposition is required for a cliff coastline to form.

List of Landforms A fjords B rias C barrier islands D mangrove coasts E sea cliffs

Match each statement with the correct option, A–E. NB You may use any option more than once.

1 Forms when glacially carved valleys are flooded by rising seas after an ice age. 2 Has a V-shaped cross-section rather than a U-shape, because a river rather than a glacier originally carved it. 3 Is made of loose sand and can change shape noticeably after a single storm. 4 Provides a sheltered nursery habitat for young fish among its submerged roots. 5 Often has a shallow underwater ridge marking where the glacier that formed it once ended. 6 Typically has a shallow lagoon lying between it and the mainland shore.