Coasts

Constructive waves

Low height, long wavelength. Strong swash, weak backwash → builds beaches.

Destructive waves

High height, short wavelength. Weak swash, strong backwash → erodes beaches.

Mechanical weathering

E.g., Freeze-thaw: Water in cracks freezes, expands, and breaks rock.

Chemical weathering

E.g., Carbonation: Rainwater (slightly acidic) reacts with limestone, dissolving it.

Biological weathering

E.g., Roots of plants or burrowing animals break rocks apart.

Hydraulic action

Waves force air into cracks, causing pressure and breaking the rock.

Abrasion

Rocks thrown by waves scrape and wear down cliffs.

Attrition

Rocks collide, breaking into smaller, rounder pieces.

Solution

Water dissolves soluble rocks like chalk or limestone.

Longshore drift

Waves hit the shore at an angle, swash carries sediment up the beach at an angle, backwash carries sediment back down perpendicular to the coastline.

Deposition

Occurs when waves lose energy (e.g., in sheltered bays, low-energy environments).

Sliding

Material moves down a slope in a straight line.

Slumping

Saturated soil/rock slides down a curved surface.

Rockfalls

Fragments of rock break off (often due to freeze-thaw weathering) and fall.

Hard rock

E.g., granite: Forms headlands and cliffs due to resistance to erosion.

Soft rock

E.g., clay: Erodes quickly, forming bays.

Concordant coasts

Rock layers run parallel to the coast, creating coves.

Discordant coasts

Rock layers are at right angles, forming headlands and bays.

Headlands and bays

Form on discordant coasts due to differential erosion.

Cliffs and wave-cut platforms

Waves erode the base of cliffs, causing collapse, leaving a platform.

Caves, arches, stacks, and stumps

Crack → Cave → Arch → Stack → Stump (e.g., Old Harry Rocks, Dorset).

Beaches

Formed by constructive waves depositing sand/shingle.

Sand dunes

Sand blown inland, trapped by vegetation (e.g., marram grass).

Spits

Long, narrow ridges of sand/shingle extending into the sea (e.g., Spurn Head).

Bars

Spits that grow across a bay, trapping water behind to form a lagoon.

Dorset Coast (Jurassic Coast)

Erosion: Durdle Door (arch), Lulworth Cove (cove), Old Harry Rocks (stack/stump). Deposition: Chesil Beach (tombolo), Studland Bay (sand dunes).

Hard engineering

Sea walls: Protect cliffs but expensive and can cause erosion downstream.

Rock armour (rip-rap)

Absorbs wave energy but looks unnatural.

Groynes

Prevent longshore drift but starve beaches downstream.

Soft engineering

Beach nourishment: Adds sand but needs regular maintenance.

Dune regeneration

Protects land but easily damaged.

Lyme Regis (Dorset)

Reasons: Protect historic town from erosion and landslides. Strategy: Sea walls, rock armour, beach nourishment.