Coastal landforms formed by erosion processes

Erosion by waves and weathering shapes the coastline, creating distinct landforms over time. These features result from the relentless action of the sea wearing away the land, often targeting weaker areas of rock.

Erosional landforms and their characteristics

• Cliffs and wave-cut platforms - Cliffs are steep rock faces formed as waves erode the base of the land. Over time, a notch forms at the high water mark, enlarging into a cave. When the unsupported rock above collapses, the cliff retreats, leaving a flat, eroded surface called a wave-cut platform.
• Headlands and bays - These form where bands of hard and soft rock lie perpendicular to the shore. Soft rock erodes faster, creating indented bays, while harder rock resists erosion, jutting out as headlands.
• Caves, arches, and stacks - Weak spots in cliffs, such as joints, erode to form caves. If caves on both sides of a narrow headland meet, an arch is created. When the arch collapses, an isolated rock pillar known as a stack remains.

Stages of formation for cliffs and wave-cut platforms

1. Waves attack the base of the cliff at the high water mark, forming a small notch through erosion.
2. The notch deepens into a cave as erosion continues.
3. The rock above the cave becomes unstable and collapses due to lack of support.
4. The cliff retreats further with repeated cycles of erosion and collapse.
5. A flat wave-cut platform is left behind as the cliff recedes over time.

Coastal landforms created by deposition processes

Deposition occurs when the sea drops sediment along the coast, building up new landforms. These features are often associated with constructive waves that carry and deposit material rather than eroding the shore.

Depositional landforms and their characteristics

• Beaches - Formed by sediment deposited by constructive waves, beaches vary by material. Shingle beaches, made of larger pebbles, are steep and narrow, while sand beaches, with finer particles, are wide and flat.
• Spits - These are long, narrow ridges of sand or shingle extending from the coast, often forming where the coastline changes direction, such as at river mouths. Longshore drift deposits material, creating a spit that may curve due to changing wind or wave directions.
• Offshore bars and tombolos - Bars are ridges of sediment that can connect two headlands or form offshore. A tombolo is a specific type of bar linking the mainland to an island, often a stack.
• Barrier islands - Long, narrow islands of sand or gravel run parallel to the coast, detached from it. They form in areas with abundant sediment, gentle offshore slopes, and moderate wave energy, often sheltering lagoons or marshes behind them.
• Sand dunes - Created when wind moves sand up the beach, accumulating around obstacles like driftwood. Vegetation stabilises the sand, forming small embryo dunes that grow into larger, mature dunes over time, sometimes reaching significant heights.
• Estuarine mudflats and saltmarshes - Found in sheltered, low-energy areas like river estuaries, mudflats develop from deposited silt and mud. Vegetation colonises these areas, trapping more sediment to form saltmarshes that remain exposed for longer between tides.

Key features and formation stages of erosional landforms

Erosional landforms evolve through distinct stages driven by wave action and weathering.

Detailed features of headlands and bays

• Differential erosion - Soft rock erodes more rapidly than hard rock, leading to the indented shape of bays and protruding headlands.
• Wave refraction - Waves bend as they approach the shore, concentrating energy on headlands and dispersing it in bays, enhancing the erosion contrast.

Formation sequence for caves, arches, and stacks

1. Waves exploit weaknesses in cliff rock, such as cracks or joints, eroding them into small caves.
2. Continued erosion enlarges caves, sometimes penetrating a narrow headland from both sides to form a natural arch.
3. The arch weakens over time, collapsing due to gravity and wave action, leaving a standalone stack.
4. Stacks may further erode into smaller stumps as wave action persists.

Key features and formation stages of depositional landforms

Depositional landforms are built by the accumulation of sediment, shaped by wave and wind action. Their development often follows predictable patterns based on coastal dynamics.

Specific features of beaches

• Berms - Small ridges of sand or shingle, typically 1-2 metres high, marking the high tide line.
• Runnels - Shallow grooves in the sand parallel to the shore, created by water draining back to the sea.
• Cusps - Semi-circular indentations on mixed sand and shingle beaches, formed by wave action.

Formation and types of spits

• Simple spit - A straight extension of sediment roughly parallel to the coast, formed by consistent longshore drift.
• Compound spit - Features multiple curved ends (recurved ends) due to periodic shifts in dominant wind or wave direction, creating a complex shape over time.
• Sheltered areas behind spits - Often develop into calm mudflats or saltmarshes as wave energy is reduced.

Formation theories for barrier islands

• Post-ice age theory - Suggests that after the last ice age, rising sea levels flooded coastal areas, moving sand offshore to form islands in shallow waters.
• Bar erosion theory - Proposes that barrier islands were once bars connected to the coast, later eroded in parts, creating separated islands with breaches.

Development stages of sand dunes

1. Wind transports sand up the beach, where it accumulates around obstacles like vegetation or debris.
2. Plants such as marram grass colonise the sand, stabilising it and forming small embryo dunes.
3. More sand accumulates as vegetation traps it, allowing dunes to grow taller.
4. Older dunes migrate inland over time, while new embryo dunes form closer to the shore, with mature dunes potentially reaching heights of up to 10 metres.

Formation process of mudflats and saltmarshes

1. Fine silt and mud are deposited in low-energy environments, such as estuaries, forming mudflats.
2. Salt-tolerant vegetation colonises the mudflats, trapping additional sediment.
3. The surface builds upwards, creating a saltmarsh that is exposed for longer periods between tides.
4. Tidal currents or streams carve channels through the surface, some of which may remain flooded even at low tide.