Coastal landscapes

 

Inhoud:

Coastal processes:

A.. Coastal erosion (= kusterosie )

B. Longshore drift / Transportation (= kustdrift)

C.. Coastal deposition (= kustsedimentatie )



Landforms of coastal erosion (= Terreinvormen door kusterosie):

1. Cliffs

2. Headlands and bays (= kapen en baaien)

3. Caves, arches and stacks (= grotten, rotsbogen en klippen)


Landforms of coastal deposition (Terreinv. door kustsedimentatie):

1. Beaches

2. Spits, bars and tombolos
... (= Sandhaken (Duits) , Nehrungen (Duits) en tombolo's (Ned.))

 

 

.

 

 

Coastal processes:
.........
A. Coastal erosion (= kusterosie)
B. Longshore drift / Transportation
(= kustdrift).
C. Coastal deposition
(= kustsedimentatie)

 


A. Three processes of coastal erosion
.
Waves that have a lot of energy are able to erode the land at the
coast.

Waves erode the land by three main processes:

1. Hydraulic action:
This is the power of the waves crashing (brekend) against the cliffs.
This forces air between cracks in the rock, which make the cracks wider
and longer until pieces of rock break off.

2. Abrasion: (= abrasie) ( abradere = afkrabben).
This is when the sand and shingle that waves are carrying are hurled
(gesmeten) against the cliff, causing pieces of rock to eventually break
off.
(It is sometimes described as sandblasting).

3. Solution (= oplossing):
This is the process of chemicals in sea water, such as salt, slowly dis-
solving minerals in the rock.

The rocks that break off the cliff and lie on the beach are then picked up
by other waves and used to abrade the cliff even more.
The rocks themselves are broken up into smaller and more rounded
pieces.

Fig: Hydraulic action of waves.

Daar de werking van de golfbeweging ondiep is, is ook de werking van
de erosie van de golven nooit dieper dan enkele meters onder de laagwaterspiegel.
Waar een kustklif door de werking van de branding achteruitwijkt, vormt
zich daardoor een abrasieplatform (brandingsterras).


Kimmeridge Bay: aan de voet van de kliffen is door de branding een brandingsterras
.. of abrasieplatform ( Engels: wave-cut platform ) ontstaan.
Bij laagwater valt het gedeeltelijk droog.




B. The process of longshore drift .(kustdrift)
......
( sedimenttransport evenwijdig aan de kust )


Longshore drift (= Kustdrift):
Sedimenttransport evenwijdig aan de kust vindt zowel plaats
over de zeebodem als over het droge strand.
Over de zeebodem wordt het veroorzaakt door golfslag en stroming
langs de kust;
op het droge strand door de wind.
Doordat de golfslag meestal iets schuin op de kust staat en doordat
afgezet materiaal daarna bovendien op het droge strand door de wind
wordt verplaatst, heeft er bij veel eenzijdige windrichting een voort-
durende materiaalverplaatsing plaats langs de kust. Dit noemt men
kustdrift
.


When a wave breaks near the shore and runs up the beach,
it is called swash
(= golfoploop).
When it runs back down the beach into the sea,
it is called backwash
(= golfterugloop).

Along many of our coastlines the swash ( golfoploop) runs up the beach
at an angle
(= scheve golfoploop) (see fig. below) .
As it has some energy it picks up sand and shingle (point A in Fig. below)
and takes them up the beach (point B).
But it does not run back along the same route. Instead the backwash
( golfterugloop) run back to the sea down the steepest slope
(volgens de grootste hellingshoek, dus loodrecht op het strand).
The backwash carries the sand and shingle with it, which it deposits
where it loses energy (point C).

The swash from the next wave then picks up the same particles and
runs them up the beach at an angle (to point D) and the backwash
returns them down the steepest slope (to point E).

In this zizzag way sand and shingle are transported along a beach.
The process is called longshore drift
(kustdrift) and it takes place in the direction of the prevailing wind.

Longshore drift carries material along a beach in a zigzag fashion in the direction
.. of the
prevailing wind.
The swash
( scheve golfoploop ) carries material both up and along the beach, while
.. the backwash ( golfterugloop ) only carries material down the beach.



 

C. The process of coastal deposition
...... (kustsedimentatie)
.
The coastline of the British Isles is being worn away, but this does not
mean that the land will eventually disappear.
The material that waves erode is deposited and it builds up land
elsewhere.

Waves deposit in areas where they have very little energy and
cannot transport all the material they are carrying.
They deposit the largest particles first, so the material is sorted
according to size.

 

.

 

 

Landforms of coastal erosion:
...
1. Cliffs
2. Headlands and bays
(= kapen en baaien)
3. Caves, arches and stacks
( grotten, rotsbogen en klippen)

 



1. Cliffs
.
Waar een kustklif door de werking van de branding terugwijkt, vormt
.. zich een abrasieplatform (brandingsterras).
.. Zo'n brandingsterras helt slechts een klein beetje zeewaarts en je
...moet
dan ook vele tientallen meters de zee in lopen voordat je kopje
.. onder gaat.

De tekeningen hieronder tonen de situatie bij hoogwater.
..
Bij laagwater valt het abrasieplatform (brandingsterras ) gedeelte-
.. lijk droog.
...
( Dit laatste geldt niet voor de Oostzee. Daar heeft men vrijwel geen
..... eb en vloed en blijft het brandingsterras onder water.)


In places where high land reaches the sea, cliffs form.
Here they are attacked by waves that are constantly crashing
(te pletter
slaan) against them and eroding them by hydraulic action, abrasion
and solution.

1. The waves mostly attack the base of the cliff, which then gets worn
away fastest, so that a wave-cut notch
( brandingsnis) begins to form
( stage 1)

2. As the waves continue to pound away at the foot of the cliff,
the wave-cut notch becomes wider and deeper ( stage 2) until the rock
above begins to crack.

3. In time, pieces of rock fall off and then the whole cliff above it
collapses into the sea.

The backwash
(golfterugloop) carries the rubble towards the sea
( stage 3).

As the cliffs erode back, a gentle sloping rock surface is left in front
of them, called a
wave-cut platform ( abrasieplatform, brandingsterras).
( Wave-cut platform = a flat area of rock eroded by waves between the
high and low tide marks. )
The type of rock and its hardness will dictate the angle of the cliff.
Chalk
(krijt) and Sandstone tend to retain a fairly vertical profile,
whereas cliffs with softer rock such as sand and clay slump
(schuiven af)
when they are undercut by the sea.

............ Fig. Stages in cliff erosion.


Happisburgh, Norfolk: one of the fastest stretches of eroding coastline in Britain.
Erosion is a problem where homes are close to the cliff edge, for example at
...Happisburgh. Sea defences can be used to protect these areas.

Zie voor coastal erosion ook: www.bgs.ac.uk/landslides/happisburgh.html


Kimmeridge Bay met haar wave-cut platform (= abrasieplatform, brandingsterras)
.. bij laagwater.



2. Headlands and bays (= kapen en baaien)
.
Like other agents of erosion, waves can erode soft rocks more quickly
than they can erode more resistant ones.
Headlands and bays are formed when the sea attacks a section of
coast with alternating bands of soft and harder rock.
The bands of soft rock, such as sand and clay, erode more quickly than
those of more resistant rock, such as limestone
( kalksteen) and chalk
(= krijt).
This leaves a section of land sticking out into the sea called a headland

(= kaap)
The areas where the soft rock has eroded at a quicker rate are called
bays.


limestone ( kalksteen) = a rock made up mainly of calcium carbonate.
chalk ( krijt) = a fine-grained limestone composed to a large extent of
......................... microscopic plankton which have slowly compacted into
......................... huge beds of chalk.

Fig. Headlands and bays:. The more resistant rocks form cliffs and headlands,
.............. ............................... the softer rocks bays with beaches at their back
.

.............................................. (Beach = sediment (pebbles, sand, mud) deposited by the sea
.............................................. along the shoreline.)

.
..In dit kaartje gebruiken we hard en soft in relatieve zin.
.. T.o.v. de betrekkelijk zachte of losse gesteenten zand en klei zijn kalksteen en krijt
.. hard, maar t.o.v. het veel hardere graniet en gneis zijn ze zacht.
.. We hebben dus de volgende reeks:
.. Zacht
( zand en klei); middelhard ( kalksteen en zandsteen); hard ( graniet en gneis).



3. Caves, arches and stacks
......... ( grotten, rotsbogen, klippen )
.
1. Once headlands and bays form, the headlands then receive the full
impact of the waves. The waves pound
(beuken) against all sides and
erode first the weakest parts of the headland. These are the places
where the cliffs have cracks
(= scheuren).
By hydraulic action and abrasion the waves make the cracks wider
(stage 1).

2. In time, this weak area will be eroded more and more until a cave
(= grot) forms (stage 2).

3. The waves now batter away at the back of the cave until they cut
through to the other side of the headland and the cave becomes an
arch
(rotsboog) ( stage 3 )

4. The rock around the bottom of the arch is now attacked by waves so
that it becomes wider. Meanwhile, the rock above the arch becomes
more unstable.
Cracks appear and, in time, the rock above collapses. This leaves a
rocky pillar
(zuil) separated fom the headland, called a stack ( klip)
(stage 4), which will itself eventually collapse.

( A Stack (= klip) is a pillar of rock (rotspilaar, rotszuil), cut off from land
by wave erosion.

The waves continue to erode in this way, widening cracks, forming caves
and making arches and stacks, until the headland is completely worn
back and the coastline becomes straight again.

Fig: Stages in the erosion of a headland.

 


.

 


Landforms of coastal deposition:
(= kustsedimentatie)
..9
1. Beaches
2. Spits, bars and tombolos

.


1. Beaches
.
The beach is the zone of deposition between high and low tidal limits,
which shelves downwards
(= geleidelijk aflopen) towards the sea.

- Beaches form where the waves have little energy so that they
.. deposit
the shingle
(kiezels), sand, silt and mud that they have been
.. carrying.
- The largest beaches are usually found in bays, where the waves are
.. generally weak.
- Beaches are made up of rock fragments that have been eroded from
.. cliffs and then broken up into smaller pieces and rounded off.
- Sometimes they have been carried along the coastline by longshore
.. drift
(kustdrift).

The swash ( golfoploop) carries particles of all sizes up a beach.
When the backwash
( golfterugloop) returns to the sea it loses energy travelling down a gentle slope.
As it loses energy, it deposits first the largest particles (shingle)
The mud and silt are smaller and can be carried much nearer to the sea
before they are dropped.

- If a beach is very steep the backwash will have more energy and so
.. might only deposit shingle
( kiezels) before reaching the sea.
- On more gentle sloping beaches, where the backwash has litle energy,
.. not only shingle, but also sand, silt and mud may be deposited.

........ Fig. Section across a beach.
........... A typical beach has sorted deposits:
........... - largest particles ( shingle) are found at the back of the beach and
........... - smallest ones (mud and silt) next to the sea.


 


2. Spits, Bars and Tombolos
Spits .
Longshore drift is the process by which material is carried along a beach.
It is responsable for the formation of several coastal features
(= kustvormen).


Spit ( = Sandhaken (Duits) ; Schoorwal (Ned.)
( = een lange, smalle landtong).
When the coastline changes abrupt direction, away from the dominant direction of longshore drift,
swash
(golfoploop) will continue to pick up sand and shingle
(see fig. point A) and deposit it in open water as it runs out of energy
(point B).
In time, it deposits enough material here for it to build up above the
level of the water.
Once this happened, the water returning to the sea as backwash at
point B will deposit some of the sand as it runs out of energy (point C).
this will also build up above sea level in time.
By this process the beach extends itself into open water and is called a
spit
(schoorwal) (stage 2)

( Schoorwal = een lange, smalle landtong).
...................... It is a strip of shingle (and/or sand) that grow out from the
...................... coast where the coastline abruptly changes direction. )

.

........... Fig. Formation of a spit (schoorwal ). Dit is een lange, smalle landtong.
.......... Shingle beach = kiezelstrand; shingle bank = kiezelwal.


Bar (= Nehrung (Duits) ; Schoorwal (Ned.) )
( = where a spit grows across a bay/estuary ).
If a spit builds out into a bay or estuary , in time it might extend
across the bay or estuary and join up with the beach on the other side
(see fig. below).
When this hapens, the coastal feature is called a bar
(= Nehrung ).
The shallow, stagnant seawater, trapped behind the bar, is called a
lagoon
(= lagune).
In time this will be filled in with wind-blown deposits, be colonised by vegetation and eventually become dry land.

......... Fig. Loe Bar, Cornwall.


Tombolo (= Tombolo (Ned.) (a bar extending out to an island).
Along some coastlines, a spit will grow outwards into open water
and reach an island
, which it then joins to the mainland (see fig. below)
This is called a tombolo
(tombolo).

........ Fig. Tombolo in northern Scotland.

The island St. Michael's Mount is also connected to the mainland by a tombolo.


Although there are examples of bars and tombolos in the Britsh Isles,
most spits do not reach very far into open water, for two reasons.
1. The water is deeper further from the shore so it takes longer to build
up material from the sea bed.
2. Many inlets have stong currents flowing into the sea (especially at
river mouths), which will take away any material deposited by longshore
drift
before it can build up above sea level.



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Nieuw venster National 4 & 5 Geography:
.... Physical Environments
 

.... Calvin Clarke and Susie Clarke, 2013
.... Hodder Gibson

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