2 - Coasts (Landforms/scapes of coastal erosion) Flashcards
(12 cards)
Fill in the blanks:
Headlands and ___ tend to form on ___ coastlines made of alternating ___ and less ___ rock, ___ to the coastline.
Strong waves ___ the coastline, quickly causing less resistant rock to form ___, leaving resistant rock protruding out to sea as ___.
bays, discordant, resistant, resistant, perpendicular, erode, bays, headlands
Fill in the blanks:
Because of wave ___, the headlands receive the highest ___ waves so are more vulnerable to ___. This encourages the formation of wave-cut ___ and then wave-___ platforms.
In the bays, energy is ___ allowing deposition of ___ to accumulate and form a ___.
Longshore currents then occur, carrying ___ from the ___ to the bays.
refraction, energy, erosion, notch, cut, dissipated, sediment, beach, sediment, headlands
Explain the formation of a wave-cut platform.
The sea creates a wave-cut notch in the base of the cliff through hydraulic action and abrasion.
Weathering weakens the top of the cliff.
The weight of the unsupported cliff causes it to collapse.
This process continues and the cliff retreats.
Backwash transports material from the base of the cliff, forming a wave-cut platform.
Explain the formation of a crack.
Cracks at the base of the headland, within the intertidal zone, become exposed through hydraulic action, which pressurises the air, forcening the crack to widen.
Cracks are further widened by weathering processes e.g. freeze thaw
Explain the formation of a cave.
Over time, cracks widen and develop as wave-cut notches.
Further processes of abrasion and hydraulic action will deepen the notch to form caves.
As a result of wave refraction, destructive waves concentrate their energy on the sides. This deepens the cave.
Explain the formation of an arch.
Wave refraction effects all 3 sides of the headland.
If 2 caves are aligned, the waves may cut through to form an arch.
Wave-cut notches widen the base of the arch.
Vertical joints are exposed by tall breakers associated with destructive waves.
Joints can also be weathered above causing blow holes to form at the roof of a cave should vertical erosion or weathering from carbonated limestone happen, forcing water through to the surface.
Explain the formation of a stack.
Over time the arch becomes unstable and collapses under its own weight to form a pillar of rock called a stack. A good example is Old Harry along the Dorset coast.
Explain the formation of a stump.
The stack is further eroded at the base creating new wave-cut notches.
Sub-aerial processes continue to weaken the stack from above.
Eventually the exposed stack will collapse to forms a stump. The broken material is further eroded through attrition and transported away to be deposited as an important supplier for bays and beaches further down the coast.
What are barrier islands?
Long narrow islands of sand or gravel that run parallel to the shore and are detached from it.
A lagoon or marsh tends to form behind the barrier island, where the coast is sheltered from wave action.
Where do barrier islands tend to form?
In areas where there is a good supply of sediment, a gentle slope offshore, fairly powerful waves and a small tidal range.
How do most scientists think barrier islands probably form?
After the last ice age ended, when the ice melt caused rapid sea level rise, the rising flow waters flooded the land behind beaches and transported sand offshore, where it is deposited in shallow water, forming islands.
Another theory is that the islands were originally bars, attached to the coast, which were eroded in sections, causing breaches in the bar.
