IGCSE Geography / Coastal environments

Caves, arches, stacks and stumps revision notes

Edexcel International GCSE Geography (4GE1), chapter 2: Coastal environments, specification point 2.1c, 2.S2. Free lesson.

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Caves, arches, stacks and stumps form in a set order as waves erode weaknesses in hard-rock headlands. Knowing the sequence and the processes at each stage helps you explain coastal landforms and use real examples.

Why these landforms form on headlands

A headland is hard rock that sticks out into the sea. Waves attack it from both sides, concentrating their energy on the rock and picking out weaknesses. Caves, arches, stacks and stumps form in headlands, not in bays. The sequence always follows the same order: crack, cave, arch, stack, stump.

How a crack becomes a cave, arch and stack

Hydraulic action is the force of waves pushing air into cracks in the rock. Abrasion is the wearing away of rock by material carried by waves. Together, these processes enlarge weaknesses. Weathering then helps weaken an arch roof until it collapses.

How a stack becomes a stump

Waves erode the base of a stack in the same way they undercut a cliff. This weakens the stack from below, so it collapses and leaves a low piece of rock called a stump. Hydraulic action and abrasion cut a notch around the stack's base. The stack is undercut and collapses, leaving a stump.

Real examples and GIS

Old Harry Rocks and Durdle Door are examples on the coast of Dorset, England. A GIS (geographic information system) stores map data in layers over one base map. You can switch layers on and off, compare them and measure from them. Old Harry Rocks are at Handfast Point, near Studland. The rock is chalk. Old Harry is the stack and Old Harry's Wife is the stump. Durdle Door is an arch cut through limestone, in Portland limestone. Coastal GIS layers might show rock type, landforms and sea defences. Cliff lines from different years can be compared to measure how fast the coast is…

How to explain stack formation for marks

For a four-mark explanation, give the landforms in order and name the process at each step. Link each cause to its result, for example by explaining that the cave breaks through the headland to form an arch.

More lessons in Coastal environments

• Waves and coastal erosion
• Longshore drift and coastal deposition
• Weathering and mass movement on the coast
• Headlands, bays, cliffs and wave-cut platforms
• Beaches, spits and bars
• Geology and the shape of the coast
• Vegetation, people and sea-level change
• Coastal ecosystems: coral reefs and mangroves
• Coastal ecosystems: sand dunes and salt marshes
• Inside one coastal ecosystem: the Sundarbans mangrove
• Coastal ecosystems under threat
• Case study: managing the mangrove
• Conflicts at the coast
• Why coasts flood
• Predicting and preventing coastal flooding
• Hard engineering at the coast
• Soft engineering and shoreline management plans
• Case study: coastal management in The Gambia
• Case study: coastal management in Sri Lanka
• Case study: coastal management in the UK
• Coastal fieldwork: collecting the data
• Coastal fieldwork: results, conclusions and evaluation