What are the landforms resulting from erosion?

Step 1: Read the key terms list below. Make sure that you understand and could give a definition to somebody else.

Step 2: Read the information in Section 1. Answer the exam questions here: 7.4 – Erosion landforms and complete the short quiz below.

Coastal unit key terms

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Key terms

Headland: A high point of land, often with a sheer drop, that extends out into a body of water. A headland of a particularly large size is known as a Cape. A headland is a ‘Promontory’ meaning that the land is raised with an abrupt decline on one side.

Bay: A bay is a body of water formed as a result of an indentation in the coastline between headlands. A beach is commonly found in a bay. A particularly large bay may be known as a gulf, sea or sound. A particularly small bay may be known as a cove.

Wave-cut platform: A wide, sloping rocky surface found at the base of a cliff.

Wave-cut notch: A small ‘notch’ cut into a cliff at the height of high tide as a result of erosion.

Cave: A landform created from erosion resulting in a hollowed-out feature at the base of a cliff.

Arch: A headland which has been partially broken through as a result of erosion leaving being an arch-shaped landform.

Stack: an isolated column or tower of rock cut off from a headland as a result of coastal erosion.

 

Section 1: Headlands and bays

baysandheadlandsbefore

A discordant coastline

Alternate bands of hard and soft rock (discordant) mean that coastal erosion happens at different rates. Hard, more resistant rock such as Chalk erodes much slower than soft, less resistant rock such as boulder clay.

Over time, the less resistant rock is worn away and retreats, leaving ‘inlet’ areas in between areas of resistant rock resulting in the formation of bays.

baysandheadlandsafter

Headlands jutting out into the sea are more vulnerable to erosion through wave action. Bay areas are more sheltered, the waves are less powerful and therefore a beach tends to form as a result of deposition.

Scarborough South Bay

Scarborough South Bay

Cliffs and wave-cut platforms

Wave-cut platform at Southdown, South Wales

Wave-cut platform at Southdown, South Wales

When waves break against a cliff, erosion takes place near to the high tide level of the cliff. Over time this results in a chunk or bite in the cliff known as a wave-cut notch. Over hundreds of years 9in most cases) the wave-cut notch deepens due to continued erosion. Eventually, the notch becomes so big that the cliff material above can no longer support its own weight and collapses.

Wave-cut notches continually forming and cliffs collapsing, eventually causes the cliff line to retreat. In place of the cliff will be a gently sloping, rocky platform known as a wave-cut platform.

Wave-cut platform formation

Wave-cut platform formation

Abrasion usually means that wave-cut platforms are smooth, but can often also contain rock pools.

Rock pools in Santa Cruz, Califonia

Rock pools in Santa Cruz, Califonia

During long periods of constructive waves, the wave-cut platform may get covered by sand. Destructive waves remove the beach once again, revealing the wave-cut platform.

Caves, arches and stacks

Lines and bands of weakness in a headland can make it vulnerable to erosion. These are known as joints or faults.

  1. Erosion can cause a line of weakness to become ‘gouged’ out, resulting in a cave forming.
Coastal cave, USA

Coastal cave, USA

2. Over time, continued erosion can lead to two back-back caves in a headland breaking through to form an arch.

Durdle Door, Jurassic Coast, South west England

Durdle Door, Jurassic Coast, South west England – notice the obvious arch formation in the headland

3. Over time, the arch is eroded at its base and sides and experiences sub-aerial weathering (from above). Eventually the roof of the arch collapses, leaving an isolated column or pillar of rock on its own in the sea. This is known as a stack.

Old Harry rocks, Jurassic Coast, Swanage, Dorset.

Old Harry rocks, Jurassic Coast, Swanage, Dorset.

Headland sequence

Headland sequence