.
......... COASTAL . LANDSCAPES....

De zee neemt en de zee geeft..
(De Norfolk Coast is een mooi voorbeeld van kusterosie en - sedimentatie):

Kusten zijn altijd in beweging:
ze kunnen afslaan of aangroeien.
(Ze kunnen ook stabiel blijven, maar dat is uitzonderlijk. Stabiliteit is meestal te danken aan de mens, die strandhoofden aanlegt en zand spuit).

The position of the coastline is constantly changing.
a. in places land is being lost to wave erosion.
b. along other parts of the coast land is being gained by deposition (=sedimentatie, afzetting).

Between the two, waves are transporting eroded materials by longshore drift (kustdrift).

A. Area of erosion: the low, crumbling cliffs
(hier dus kustafslag)
• The main sections with cliffs are shown in the map below.
• Those near Hunstanton are sandstone capped by chalk (=krijt). Dit is relatief zacht materiaal, dus sterke erosie.
• Those on both sides of Cromer are glacial till (boulder clay) (=keileem ; grondmorene). This is the so called Cromer Ridge.
Dit is een beboste morenewal die tussen Cromer en Holt ligt.
Diverse gletsjers hebben hier lange tijd hun eindpunt gehad, waardoor veel materiaal zich kon ophopen. De aldus ontstane rug is meer dan 100 m hoog en bestaat uit materiaal variërend van klei tot rotsblokken.
Boulder clay is susceptible to erosion as it is weak in relation to other rocks. Wave action easy removes the clay. The larger stones then tumble down due to their weight.

B. Area of deposition (sedimentatie, afzetting) : the coastal plain (hier dus kustaangroei).
• Sedimentatie vindt plaats bij het grootste deel van dit langeafstandspad, het hele middengedeelte. Hier hebben we een kustvlakte met:
- brede stranden en daarachter duinen,
- wadden en kwelders,
- een barrière-eiland (Scolt Head Island) en
- een lange shingle spit (kiezel-schoorwal) bij Blakeney.
• A study of beach deposition (sedimentatie, afzetting) reveals a change in direction of the .longshore drift (kustdrift) west of Sheringham (see map).
The effects of big waves hitting the coast from the dominant northerly and .north-easterly directions is thought to be responsible for causing the local.direction of the littoral drift (kustdrift) to go from east to west towards .the Wash, contrary to the national trend.

Hoofdstuk1
Kustprocessen:
A. Coastal erosion (kusterosie)
.
Waves that have a lot of energy are able to erode the land at the coast.
Waves erode the land by 3 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. (Sometimes described as sandblasting (zandstralen)).

3. Solution (=oplossing):
This is the process of chemicals in sea water, such as salt, slowly dissolving 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 door de golven nooit dieper dan enkele meters onder de laagwaterspiegel.
Waar een kustklif door de werking van de branding achteruitwijkt, vormt zich daardoor een brandingsplatform.


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

Hoofdstuk3
Kustprocessen:
Longshore drift/ Transportation
(= kustdrift) (= sedimenttransport evenwijdig aan de kust)
Sedimenttransport evenwijdig aan de kust vindt zowel plaats over de zeebodem (1) als over het droge strand (2).
1. Over de zeebodem wordt het veroorzaakt door golfslag en stroming langs de kust.
2. Op het droge strand door de wind.
Doordat de golfslag (1) meestal iets schuin op de kust staat en doordat afgezet materiaal daarna bovendien op het droge strand door de wind (2) wordt verplaatst, heeft er bij veel eenzijdige windrichting een voortdurende materiaalverplaatsing plaats langs de kust. Dit noemt men kustdrift.

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. .....

Hoofdstuk3
Kustprocessen:
B. 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
.
(= Landvormen door kusterosie):
1. Cliffs,
2. Headlands and bays,
3. Sea caves, sea arches, sea stacks.

Hoofdstuk4
Landvormen door kusterosie:
1. Cliffs
.
Waar een kustklif door de werking van de branding terugwijkt, vormt zich een brandingsplatform.
Zo'n brandingsplatform 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 brandingsplatform gedeeltelijk droog.
(Dit laatste geldt niet voor de Oostzee. Daar heeft men vrijwel geen eb en vloed en blijft het brandingsplatform 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 (de voet) 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 (=brandingsplatform).

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 (klifrand), for example. at Happisburgh.. Sea defences can be used to protect these areas.
See for coastal erosion also: www.bgs.ac.uk/landsli

Kimmeridge Bay met haar wave-cut platform (=brandingsplatform) bij laagwater. .....

Hoofdstuk5
Landvormen door kusterosie:
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.

Fig. Headlands and bays:
- The more resistant rocks form HEADLANDS with CLIFFS,
- the softer rocks form 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). .....

Hoofdstuk6
Landvormen door kusterosie:
...(brandingsvormen)
3. Sea caves, sea arches, sea stacks
....brandingsgrotten,
... brandingsbogen,
... brandingspilaren
.
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 (stage1).

2. In time, this weak area will be eroded more and more until a sea cave (=brandingsgrot) forms (stage2).

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 sea arch (=brandingsboog) (stage3)

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 (= pilaar) separated fom the headland (= kaap) , called a sea stack (=brandingspilaar; klip) (stage 4), which will itself eventually collapse.

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.

Video: www.youtube.com

Fig: Stages in the erosion of a headland (=kaap).

Hieronder geef ik de Duitse namen:
Wil je ook de heldere Duitse tekst daarbij zien, ga dan naar:
www.spektrum.de/lexiko en typ in het zoekvenster: Brandungsformen.
Klik vervolgens in de Suchergebnisse op Brandungsformen.

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

Hoofdstuk7
Landvormen door kustsedimentatie
1. Beaches

- 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 ravelling 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. .....

Hoofdstuk8
Landvormen door kustsedimentatie:
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).

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)

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

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 egetation and eventually become dry land.

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

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.

Weet je aanvullingen en verbeteringen van deze tekst?
Graag een e-mail naar:

.... ..... ...

...

LAATST BIJGEWERKT : 13-4-2022 ...