KS3 coasts: erosion, landforms and management for parents

Coastal processes and landforms, explained

Waves are made by wind blowing over the sea. Their size depends on the strength of the wind, how long it blows and the fetch, which is the distance of open water it blows across. A long fetch, as on the south-west coast of Britain facing the Atlantic, produces large, powerful waves. When a wave breaks, the water rushing up the beach is the swash and the water draining back is the backwash. Constructive waves are low and gentle, with a strong swash and weak backwash, so they build up beaches. Destructive waves are tall and steep, with a strong backwash, and they tend to remove material and erode.

Pupils learn four main erosion processes. Hydraulic action is the force of water pounding into cracks, compressing the air inside and widening them. Abrasion is waves hurling sand and pebbles at the cliff. Attrition is rocks and pebbles carried by the waves knocking against each other until they become smaller and rounder; it wears down the load rather than the cliff itself. Solution is the dissolving of rocks such as limestone by seawater. Weathering and mass movement, such as rockfalls and slumping, also work on cliffs from above. Hard rock such as granite resists erosion better than soft clay, so geology influences the shape of the coast.

Material is moved along the coast by longshore drift. Waves usually approach the beach at an angle, set by the wind direction. The swash carries material up the beach at that angle, but gravity pulls the backwash straight down the slope, so pebbles and sand zigzag along the shore. Where the coastline changes direction or a river mouth interrupts the flow, material is deposited. This can build a spit, a long finger of sand or shingle that extends out from the coast, and sometimes a bar across a bay.

From these processes pupils explain landforms in sequence. On a headland, waves attack a crack and widen it into a cave. If the cave cuts through the headland it becomes an arch. When the arch roof collapses, a stack is left, and this in turn is worn down to a stump. Cliffs retreat as waves cut a notch at the base until the rock above collapses. As this repeats, the cliff moves back inland, leaving a gently sloping wave-cut platform that shows at low tide. Headlands and bays form where bands of hard and soft rock meet the sea: the soft rock is worn back into bays and the hard rock is left sticking out as headlands. The programme of study does not name places, so schools choose their own examples, such as the Dorset coast, the Holderness coast in East Yorkshire or the Norfolk coast.

The last strand is management. Hard engineering includes sea walls, rock armour and groynes, which are wooden or rock barriers that trap sand. Soft engineering works with nature, for example beach nourishment, which means adding sand or shingle, and dune restoration. Managed retreat means allowing the sea to flood land that is not worth defending. Pupils weigh costs, benefits and who is affected, because protecting one place can change erosion elsewhere. This fits the aim of understanding how geographical processes create landscapes that change over time.

Words your child will hear

Fetch

The distance of open water over which the wind blows to make waves.

Swash and backwash

The movement of water up the beach after a wave breaks, and back down again.

Hydraulic action

Erosion by the force of water and compressed air in cracks in rock.

Longshore drift

The zigzag movement of sand and pebbles along a beach.

Wave-cut platform

A flat rocky area at the foot of a cliff, left as the cliff retreats.

Groyne

A barrier built out into the sea to trap sand and slow longshore drift.

Managed retreat

Deliberately allowing the sea to flood or erode an area that is not defended.

What the National Curriculum says

The programme of study for Key Stage 3 says:

• Pupils should be taught to understand, through the use of detailed place-based exemplars at a variety of scales, the key processes in physical and human geography
• Physical geography relating to: geological timescales and plate tectonics; rocks, weathering and soils; weather and climate, including the change in climate from the Ice Age to the present; and glaciation, hydrology and coasts
• Pupils should understand how geographical processes interact to create distinctive human and physical landscapes that change over time.

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

A model answer: how is a stack formed?

Common mistakes and how to help

How to help at home

• Read a pebble beach. On a beach visit, pick up a few pebbles and compare their shape and size. Smooth, rounded stones have been worn down by attrition over a long time, whereas sharp, angular ones have usually not been worn for as long. Check the tide times, stay well away from the foot of cliffs and leave the pebbles on the beach.
• Spot the management. Look for groynes, sea walls, rock piles and dune fences. Ask your child what each is meant to do and who it protects. Look at which way sand has built up against a groyne to show the direction of longshore drift.
• Make a wave tank. Use a large shallow tray with a slope of sand at one end. Tilt the tray gently or push water with a flat board to make waves, and compare gentle waves with sharp ones. Do this outdoors, supervised.
• Sketch a headland and bay. Look at a coastal map and find a place where a headland alternates with a bay. Ask your child where the rock is likely to be harder and where softer, and how erosion would change the shape over time.
• Check the safe distance. Look at warning signs on cliffs and read why they are there. Talking about rockfalls and unstable edges is a useful link between the geography and staying safe on holiday.

Related topics

Everything in Key Stage 3 geography