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Unlock This CourseImagine a giant sculpture being slowly carved by the sea over thousands of years. That's exactly what happens when waves attack our coastlines! Stack and stump formation is one of the most dramatic examples of coastal erosion in action. These towering rock pillars and stumpy remains tell an amazing story of the power of the sea.
Stacks and stumps are found along coastlines where hard rock meets the relentless force of waves. They're particularly common around the UK, where our varied geology creates perfect conditions for these spectacular landforms to develop.
Key Definitions:
Stack and stump formation follows a predictable sequence that can take thousands of years. It all starts with a headland - a piece of hard rock sticking out into the sea. Waves attack this headland from all sides, but they're particularly powerful during storms when they can reach heights of over 30 metres!
The formation of stacks and stumps is like watching nature's own demolition project in super slow motion. Each stage builds on the last, creating increasingly dramatic landforms until gravity finally wins.
Everything starts when waves find a weakness in the headland. This could be a crack in the rock, a joint, or an area where the rock is slightly softer. The waves use four main processes to attack these weak spots:
Waves crash into cracks and compress the air inside. When the wave retreats, the air expands explosively, widening the crack bit by bit.
Waves pick up rocks, pebbles and sand, hurling them at the cliff face like natural sandpaper, wearing away the rock.
Seawater is slightly acidic and can dissolve certain types of rock, particularly limestone and chalk.
Over hundreds of years, these processes hollow out a cave in the headland. The cave grows deeper and wider as waves continue their relentless attack.
As the cave gets deeper, waves may start attacking the headland from the other side too. If two caves meet, or if one cave is eroded right through the headland, an arch forms. This creates one of the most spectacular coastal landforms - a natural bridge of rock spanning the gap.
Arches can be massive structures. Some are large enough for boats to sail through, whilst others are more like windows in the rock. The size depends on the type of rock and how long the erosion has been going on.
Durdle Door is one of England's most photographed natural arches. Made of limestone, it has taken around 10,000 years to form. The arch is about 150 million years old, but the actual archway is much younger - a perfect example of how geological time works on different scales!
Arches look solid, but they're actually quite fragile. The roof of the arch is constantly being weakened by:
Eventually, the arch becomes too weak to support its own weight and collapses. This usually happens during a storm when the extra wave power provides the final push. When the arch collapses, it leaves behind a tall pillar of rock standing alone in the sea - this is a stack.
Old Harry Rocks are chalk stacks at the eastern end of the Jurassic Coast. There used to be several stacks here, but erosion continues. Old Harry's Wife collapsed in 1896 during a storm, leaving just a stump. Old Harry himself is about 20 metres tall and continues to be eroded at a rate of about 60cm per year.
Stacks might look permanent, but they're not! Wave erosion continues to attack the base of the stack, making it narrower and weaker. The stack also suffers from weathering - rain, wind, frost and salt spray all take their toll.
Over time, the stack becomes top-heavy and unstable. Eventually, it too collapses, leaving behind just a low platform of rock called a stump. Stumps are often only visible at low tide, appearing as flat rocky platforms surrounded by water at high tide.
Not all coastlines develop stacks and stumps at the same rate. Several factors control how quickly these landforms develop:
Hard rocks like granite take much longer to erode than softer rocks like clay. Limestone and chalk are somewhere in between - hard enough to form dramatic cliffs but soft enough to be carved by waves over geological time.
Coastlines facing the prevailing wind and exposed to long fetches experience more powerful waves. The Atlantic coasts of Scotland and Cornwall see much more erosion than sheltered areas like the Thames Estuary.
Storm frequency and intensity play a huge role in coastal erosion rates. Climate change is actually speeding up coastal erosion in many areas due to:
The UK's varied geology and exposed position in the Atlantic make it a perfect place to see stacks and stumps. Here are some of the most famous examples:
Standing 137 metres tall, this is one of the UK's most famous stacks. Made of red sandstone, it's located in Orkney and is a popular challenge for rock climbers. The stack is relatively young in geological terms - probably only a few thousand years old.
The basalt columns here create unique coastal landforms. The regular jointing in the rock creates geometric stacks and stumps that look almost artificial. The area shows how rock structure influences the shape of coastal landforms.
This chalk headland has numerous stacks, arches and caves. The area demonstrates the full sequence of coastal erosion landforms, from initial caves through to collapsed stumps.
On Ordnance Survey maps, stacks appear as small isolated areas of land surrounded by sea. They're often marked with spot heights showing their elevation. Stumps may not appear on maps if they're only visible at low tide, but the area might be marked as "rocks" or have depth soundings showing shallow water.
Stacks and stumps aren't just pretty to look at - they have real economic and environmental value:
Dramatic coastal scenery attracts millions of visitors each year. The Jurassic Coast, which includes many famous stacks and arches, is a UNESCO World Heritage Site and brings in over £1 billion annually to the local economy.
Stacks provide important nesting sites for seabirds like gannets, cormorants and puffins. The isolation protects them from ground predators, whilst the surrounding seas provide rich feeding grounds.
These landforms help scientists understand past sea levels, climate changes and geological processes. They're like natural laboratories for studying coastal erosion and rock formation.
Stack and stump formation is an ongoing process. Climate change is likely to accelerate coastal erosion through rising sea levels and more intense storms. This means we might see more dramatic collapses in the coming decades, but it also means new stacks will form as headlands continue to be eroded.
Understanding these processes helps us predict and manage coastal change, protecting both human settlements and natural environments for future generations.