Managing river and coastal environments: A continuing challenge
2.4
How do coastal
processes shape the
land?
Part B
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Blowhole
Sea arch
Geo
Stack
Sea cliff
Sea
cave
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Beach
Spit
Bar
Tombolo
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
Is wave action the
only factor in
shaping the coast?
No, there are several
factors interacting
with each other to
create coastal
landforms.
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
1
Tectonic movement
Tectonic movement can
cause land to rise or fall.
Subject to active
wave erosion
The uplifting or lowering
of the coastline changes
the zone of active wave
erosion.
Uplifting (or
lowering) of land
Sea
Plate
Compressional
force
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
2
Nature of rocks
Horizontal bedding plane
Wave undercutting enlarges
the notch and causes
collapse of rock above the
notch. Parallel retreat of
cliffs is resulted.
Sea
Land
Notch
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
2
Nature of rocks
Bedding plane dipping seawards
Rocks loosened by
wave erosion and
mass movement slide
down along the
bedding plane.
Sea
Land
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
2
Nature of rocks
Bedding plane dipping landwards
The slope is
more resistant
to wave erosion.
Sea
Land
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
3
Weather and climate
Global warming leads to
a rise in sea levels
because of the thermal
expansion of water and
melting of polar ice caps.
Changes in sea levels
are changing the
position of the zone of
active wave erosion.
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
3
Weather and climate
A warmer world would
generate more storm
surges, thereby affecting
coastal landforms.
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
4
Fluvial processes
Rivers bring sediment to the
coast as they flow to the sea.
Delta
Deposition occurs at the
coast where wave action is
weak. Sediment may
gradually build up to form
depositional landform such
as a delta.
The River Nile, Africa (Credit: NASA)
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping
the coast?
5
Marine organisms
Some marine organisms
protect the coast from wave
erosion and favour
deposition.
For example, coral reefs and
mangroves.
Mangroves
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Sea cliffs and wave-cut platforms
Waves
The
A
Undercutting
notch
waves
repeatedly
is formed
erode
continues
the
pound
by part
undercutting.
and
against
of the coast
notch
the coast.
between
is enlarged.
high
tide and
The
overhanging
low tide. part above the notch collapses. It
forms a sea cliff.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Sea cliffs and wave-cut platforms
Over time,
Erosion
continues,
a gently sloping
the sea cliff
or flat
retreats
surface
inland.
called a
wave-cut platform is developed at the base of the
sea cliff.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Sea cliffs and wave-cut platforms
Wave-cut
platform
Ping Chau in Mirs Bay
Sea cliff
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Sea caves and geos
Block diagram
Line of weakness
Cross-section
Geo
Sea cave
Collapse of
cave roof
Land
Sea cave
Sea
High tide level
Land
Low tide level
Sea
When
A
Active
line of
waves
wave
weakness
erosion
splashinagainst
widens
the cliffthe
is roof
exposed
line of
of weakness
a narrow
to waves.
sea
to
form athe
cave,
searoof
cave.
may collapse. A geo is formed.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Sea caves and geos
A sea cave in Sai Kung
A geo in Sai Kung
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Sea arches and stacks
Whenleaves
a erosion
sea acave
gets
eroded
time
to
it
This
Further
mass
may
ofcause
rock
with
thefrom
sea
steep
arch
sides
to time,
collapse.
standing
might cut This
through
tostack.
form a sea arch.
offshore.
is the
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Sea arches and stacks
A sea arch and a stack in Canada
(Credit: Getty Images)
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Blow-holes
w
When
vertical
waves
orisnear
A
sea
cave
break into
vertical
tunnel
the
is
developed
along
sea
formed
cave,
alongline
the
a
horizontal
hydraulic
vertical
weakness
action
of
weakness.
of waves
as
a blow-hole.
takes
place along the
vertical
weakness in it.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
A
Erosional landforms
Blow-holes
During storms, waves breaking
into the sea cave may force
water or just air out of the
blow-hole.
Halona Blow-hole in
Hawaii
(Credit: Getty Images)
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Beaches
Wave energy is dispersed
in sheltered bays.
Deposition takes place to
form beaches.
Sand and shingle are
built up between the
lowest and the highest
water levels.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Beaches
Waikiki Beach, Hawaii
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Spits
Materials
The sediment
are
transported
accumulatesalong
and builds
the
coast
up intobya longshore
spit, with one
drift.
end attached to the land,
Where the coastline
and the other end
changes, the materials
extending out to the sea.
are deposited in slack
water.
The spit extends as
sediment continues to
accumulate.
Wind direction
Longshore
drift
Longshore
drift
Spit extends
Sea
Wave crest
Change of
Marshland
coastline
Land
Area are
behind the
Materials
spit
of low
built up
to is
form
mud and
aenergy,
spit
marshland
begins to
develop
Longshore drift
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Spits
As the waves are
refracted, the end of the
spit becomes hooked.
Marshland
Land
Longshore
drift
spit
Sea
End of the spit is
bent or recurved
Wave crest
A Spit in Greece (Credit: Corbis)
Longshore
drift
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Bars
When a spit develops
and extends across a
bay, a bar is formed.
A lagoon is formed
behind the bar.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Bars
(Credit: Corbis)
Chesil Beach in England is formed from a bar
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Tombolos
When the spit builds
up and joins an island
to the mainland or
two islands together,
a tombolo is formed.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal
processes?
B
Depositional landforms
Tombolos
The Cheung Chau tombolo
is formed when two spits
join together.