Film info
Film summary
Coastal erosion produces beautiful beaches and some rather unusual land formations, from spits to stacks, mud flats to salt marshes.Key facts
- Cliffs are formed when destructive waves attack the bottom of rock faces.
- Weak points in the rock give way to a hollow called a wave-cut notch.
- The cliff retreats and eventually the overhanging rock collapses, forming a wave-cut platform.
- Beaches are built up as sand, pebbles, and rocks are deposited by constructive waves.
Transcript
The continual battle between land and sea is apparent here - along the northwest coast of America - where erosion is the predominant force.
Erosion
Millions of years ago, this coastline would have looked very different.
Even though the land is tough basalt, the relentless attack of the sea has eroded it in spectacular ways.
Cliffs are formed when weathering weakens the top of the land and destructive waves attack the bottom of the rock face.
Destructive Waves
Weak points in the rock are affected most, and eventually form a hollow, called a wave-cut notch.
Wave-cut Notch
The overhanging rock collapses, and the rubble is carried out to sea, forming a wave-cut platform.
Wave-cut Platform
The whole process continues, causing the cliff to slowly - but continually - retreat.
But erosion also produces more unusual features.
Hollow caves can be carved out by the water and eventually break through, forming an arch.
The continual erosion keeps widening the arch until it can no longer support the land on top.
The arch collapses and leaves a headland on one side, and a tough outcrop of rock on the other - called a stack.
Stack
Whilst erosion constantly attacks our coastlines, deposition builds characteristic landforms.
Deposition
When constructive waves wash on to the shore, they dump material carried in the water, like sand, pebbles and rocks.
Constructive Waves
Deposition
This builds up beaches.
Whether a beach is soft and sandy or hard and pebbly depends on both the wave energy and the local geology.
A narrow, extended stretch of beach that projects out to sea is called a spit.
Spit
These are formed by deposition as well, but wind conditions also have a part to play.
Where the prevailing wind blows at an angle to the coast, it causes longshore drift.
Material is moved along the coast at an angle.
Over time, the wind and waves affect the end of the spit, causing it to curve to create a hook end.
This creates a sheltered area protected from incoming waves.
Silt is deposited, and mud flats or salt marshes can form.
Erosion and deposition have created the world's beautiful and dynamic coastline, and continue to affect these ever-changing landscapes.
