Transcript Coastal Features Headlands and Bays

Coastal Features
Headlands and Bays
Headland and Bay
headlands
animation
A headland is an area of land which juts out to sea and is surrounded by sea on
three sides. Headlands form in coastlines where there are hard rocks and soft
rocks which causes differential erosion.
Hard resistant rocks are more difficult to erode than softer rock. In places such
as the Dorset coast harder limestone rock forms headlands while softer clays
form bays.
The softer rock is eroded in three ways: abrasion is caused by waves throwing beach
materials against the cliff and corrosion when limestone is dissolved by sea water and
hydraulic action where air in a crack is compressed by the on-rushing wave and this
will force the rock to break off. Attrition is when the rock hit each other in the water and
are eroded down..
CLIFF & PLATFORM
Wave erosion is greatest where longer waves break against the foot of the cliff; this
forms a wave-cut notch.
As the notch gets bigger the cliff above is left unsupported and collapses due to
gravity.
This continues and the cliff retreats and increases in height. The gentle sloping
expanse of the retreating cliff is called a wave cut platform.
(Explain the four processes of erosion from the Headland and Bay note
)
Platform animation
Notch and Platform
Caves, Arches and Stacks and
stumps
Stack diagram
stack photos
Durdle door
old man of Hoy
1. Waves attack areas of weakness such as a joint or a fault.
2. A sea cave is formed in the headland and is deepened and widened over a long
period of time.( if choosing this feature in paper one you explain abrasion and
hydraulic action at this part)
3. The sea eventually cuts through the headland to form an arch.
4. Waves continue to erode the foot of the arch until its roof becomes too heavy
and collapses due to gravity. The roof of the arch is also eroded by freeze thaw
action causing it to collapse.
5. This leaves part of the headland cut off to form a stack.
6. The stack is then undercut by waves and collapses to form a stump.
7. Occasionally water rises up a vertical joint and is ejected as a blow hole.
Slumping
slumping
Where the sea undercuts soft clay cliffs slumps often occur.
This is also common after an earthquake.
Rapid movement of material.
A whole section of a slope gives way when unsupported rock
begins to slide.
After heavy rain the surface becomes saturated and much
heavier and liable to slide. The rain also lubricates the
underlining rock making the rock easier to slide.
Slumping
Features of Coastal Deposition
Material which is eroded from the coastline is transported by
longshore drift.
Longshore Drift
Waves approach the beach at an angle from the direction the
wind is blowing. When the wave breaks the material is carried
up the beach at the same angle at which the wave approached
the shore (swash). As the wave dies away the backwash
returns materials at right angles to the water under the influence
of gravity. Material is moved along the coast in a zig-zag
course.
Animation of longshoredrift
Where this transported material reaches an area where the water
is sheltered and waves lack energy e.g. This material is deposited
to form a beach.
Where there is a sudden change in the coastline such as in a river
estuary a long narrow length of sand or shingle extends out to the
sea to form a spit. If the spit extends or grows to reach the other
side then a sandbar is formed. These are unlikely to form if the
estuary has strong tides or the estuary is too deep.
The sea is relatively sheltered and shallow and a salt marsh is
formed behind the spit.
Saltmarsh
Spit
Bars
After the last Ice Age sea levels rose as the ice and snow
Spit melted.
stages
Many coastal areas were drowned creating Rias. A Riadiagram
is a drowned
river valley. Rias are winding valleys with gentle sides.