Coastal Processes and Landforms, Knowledge Organiser

Key Terms

• Fetch — distance of open water; determines wave energy
• Constructive wave — strong swash; builds beaches (6–8/min)
• Destructive wave — strong backwash; erodes coasts (10–14/min)
• Longshore drift — zigzag sediment movement along coast
• Wave-cut notch — groove at cliff base; precedes collapse
• Spit — ridge extending from coast change; curved tip = wave refraction
• Sediment budget — balance of sediment supply; management upstream affects coast downstream

Erosion Processes (HASA)

• Hydraulic action — air compression in cracks; pressure release fractures rock
• Abrasion — sediment as sandpaper; grinds cliff base and wave-cut platform
• Solution — acid seawater dissolves limestone and chalk
• Attrition — sediment particles round each other in transport (NOT cliff erosion)

Holderness Coast Key Facts

• East Yorkshire; 60 km from Flamborough Head to Spurn Head
• Fastest-eroding coast in Europe: average 1.7 m/year
• Cliffs: soft boulder clay — glacial deposit; no internal structure
• No beach — longshore drift removes sediment southward (~500,000 t/year)
• North Sea fetch: up to 700 km; high-energy destructive waves
• Mappleton protected (1991, £2 million rock armour + groynes)
• Consequence: increased erosion south of Mappleton — sediment budget disrupted
• 30+ villages lost since Roman times; Spurn Head spit fed by eroded material

Landform Formation Summary

• Wave-cut platform: notch → overhang → collapse → platform; widens as cliff retreats
• Headland and bay: differential erosion; hard rock remains; soft rock eroded back
• Cave → arch → stack → stump: hydraulic action exploits joint → breaks through → roof collapses → pillar → low platform
• Spit: longshore drift past coast direction change → deposition in open water → curved tip from wave refraction
• Bar: spit extending across a bay; encloses a lagoon
• Tombolo: deposition connecting mainland to island (e.g. Chesil Beach/Portland)

Common Mistakes

• Confusing constructive and destructive waves: Constructive waves have strong swash and build beaches (6–8 per minute); destructive waves have strong backwash and erode coasts (10–14 per minute) — frequency is a key distinguishing fact
• Saying attrition erodes cliffs: Attrition is sediment particles wearing each other down during transport — it does NOT erode cliff faces; abrasion and hydraulic action erode cliffs
• Forgetting the sediment budget at Holderness: The Mappleton groynes (1991) stopped sediment reaching areas south — increased erosion south of Mappleton is a direct consequence; management in one place harms another
• Omitting wave refraction in spit descriptions: The curved tip of a spit is caused by wave refraction bending waves around the end of the spit — this detail is needed for full marks on formation questions

Memory Aid

HASA — The Four Erosion Processes H — Hydraulic action — air compression in cracks → pressure release → rock fractures A — Abrasion — sediment as sandpaper → grinds down cliff face and wave-cut platform S — Solution — acid seawater dissolves limestone/chalk → chemical attack A — Attrition — sediment particles collide → get smaller and rounder → boulder to pebble to sand Remember the difference: H, A and S attack cliffs. The second A (Attrition) acts on sediment in transit — it rounds pebbles, not cliffs. CASE — Factors Affecting Erosion Rate C — Cliffs (rock type): soft clay or chalk erodes fast; hard granite resists A — Arrival of waves (fetch): long fetch = high-energy destructive waves S — Sand and beach: wide beach absorbs energy; no beach = direct cliff attack E — Engineering and climate change: sea walls and groynes change sediment budget; sea level rise accelerates everything The Headland Sequence: C — A — S — S Cave → Arch → Stack → Stump. Each stage in the destruction of a headland begins with hydraulic action exploiting a weakness and ends with the complete collapse and erosion of the remaining structure.