|
|
|
|
|
|
|
|
|
 |
Coastal Landscapes |
|
|
Why do waves
break?
|
||
|
Waves are the
result of the wind blowing over the sea.
As they approach land they break.
The
bottom of the wave touches the sand and slows down
due to increased friction. The top of the wave
becomes higher and steeper until it topples over.
|
||
 |
||
|
Types of Waves |
||
|
Constructive Waves
•These
build up the beach.
•If
the swash is stronger than the backwash, material is carried
on to the land and is deposited there.
•This
happens with low waves. They break so that the water runs
gently up the beach.
•They
usually occur on gently sloping beaches.
•They
arrive at a rate of about 6-8 waves per minute.
•They
are also called “spilling waves”.
|
||
 |
||
|
Destructive Waves
•These
remove material from the beach.
•If
the backwash is stronger than the swash, the waves erode the
coastline.
•This
happens with high steep waves which break so that the water
crashes down to the beach.
•They
usually occur on steeply slopping beaches.
•They
arrive at a rate of about 13-15 waves per minute.
•They
are also called “plunging waves”
|
||
 |
||
|
What are sub-aerial processes? |
||
|
The coast is the
narrow zone between the land and the sea.
It is worth
remembering that the landscape will be influenced by
processes on the land as well as the sea.
Sub-aerial
processes include weathering and mass movement. These
processes operate on the cliff face to weaken it and provide
material for coastal erosion.
|
||
 |
||
| Processes of erosion. | ||
|
Attrition
Materials carried
by the waves bump into each other and so are smoothed and
broken down into smaller particles.
|
||
|
Hydraulic
action
This process
involves the force of water against the coast. The waves
enter cracks (faults) in the coastline and compress the air
within the crack. When the wave retreats, the air in the
crack expands quickly, causing a minor explosion. This
process is repeated continuously.
|
||
|
Corrosion
This is the
chemical action of sea water. The acids in the salt water
slowly dissolve rocks on the coast. Limestone and chalk are
particularly prone to this process.
|
||
|
Abrasion/Corrasion
This is the
process by which the coast is worn down by material carried
by the waves. Waves throw these particles against the rock,
sometimes at high velocity.
|
||
 |
||
| Wave-Cut Platform | ||
 The
waves attack the base of the cliff through the processes of
abrasion, corrosion, hydraulic action and attrition.
Over
time the cliff will be undercut and a wave-cut notch
is formed. Eventually
the cliff becomes unstable and collapses. Further cliff
retreat will form a wave-cut platform.
|
||
 |
||
|
Longshore
drift
|
||
|
This movement of
sediment along the coastline is called longshore drift.
|
||
 |
||
|
Landforms of
coastal deposition
|
||
|
1)Beaches
2)Spits
3)Tombolos
and Bars
|
||
 |
||
|
How are
beaches formed?
|
||
|
Beaches form in sheltered environments,
such as bays between two headlands. When the swash is
stronger than the backwash, deposition occurs. (Low
constructive waves deposit material on the shore. Gradually
the beach is built.
Sometimes sand from offshore bars can be
blown onto the shore by strong winds.
Some beaches are made of shingle or pebbles. Beach
material is usually very well sorted, most of the material
on a particular beach is of a similar size.
The larger the material is, the steeper
the beach. So shingle and pebble beaches are steeper than
sand beaches.
|
||
 |
||
|
How are spits
formed?
|
||
|
Spits are long, narrow ridges of sand or
shingle running out from the coast. They form where the
direction of the coast changes. They are often found across
a bay or at the mouth of a river. They grow as material is
added by longshore drift. Many spits develop a hooked or
recurved end. Spits can change shape quite quickly. They can
be breached or destroyed by waves.
|
||
|
Conditions for a spit to form.
• Sea
must be relatively shallow.
• Must
be a good supply of sand and other material.
• Waves
must approach at an angle.
• Sea
must be fairly calm, with constructive waves.
|
||
 |
||
|
What is a
tombolo?
|
||
|
Tombolos are
ridges of sand and other material than link the mainland to
an Island a little way out to sea.
|
||
 |
||
|
What is a bar?
|
||
|
Bars are ridges of sand and other
material that run roughly parallel to the coast. They block
off river mouths and bays.
Water dammed up behind a bar is
called a lagoon. These are soon filled in by
sediment from waves breaking over the bar or from
streams flowing into the lagoon.
Off-shore bars and
barrier islands are not joined to the coast.
These bars form some way out to sea where
waves break in shallow water.
If a spit joins one part of the
mainland to another it is called a
bar.
|
||
 |
||
|
Landforms created by changes is sea level. |
||
|
Raised Beaches
•A
raised beach is an old beach now standing above sea level, a
few metres inland.
|
||
 |
||
|
Rias
•A
seaward end of a river valley that has been drowned by a
rise in sea level.
|
||
 |
||
|
Fjords
•A
fjord is a long, narrow inlet caused by the drowning of a
glaciated valley.
|
||
 |
