Coastal land forms.ppt

7/29/2019 Coastal land forms.ppt

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The Sea

Creator and Destroyer


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The action of the sea

The sea is constantly changing the shapeof our coastline.

This is happening because waves, likerivers, erode, transport, and depositmaterial.

Waves move material along our coastline.


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Why do waves break on the Shoreline?


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Waves

Waves are made because of frictionbetween the wind and the surface of the

sea.

The size of the wave depends on 2 things.

1. The strength of the wind.

2. The length of the sea (fetch).


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Waves Swash & Backwash

Swash As the wave reaches the shore itbreaks. The white foamy water that flows

up the beach is called the Swash.

Backwash When the water runs out ofspeed it stops and it flows back down thebeach into the sea. This is called thebackwash.


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Constructive waves

They have a strong Swash which transports anddeposits material on the beach.

They have a weak Backwash which does notcarry much material back to the sea.

As a result they construct/add material to thebeach.


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Constructive Waves


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Destructive waves

They have a weak Swash.

They have a very strong Backwash whichwears away and carries away materialform the beach.

Therefore, there is a lot of erosion andthey destroy/destruct the coastline.


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Destructive Waves


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Sea Erosion

Sea erosion is caused by Destructivewaves. They erode the coast in 4 ways.

1. Hydraulic Action2. Air Compression

3. Abrasion4. Attrition


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Sea Erosion

1. Hydraulic Action this is the power ofthe water hitting the coastline.

2. Air Compression The waves trap air incrack in the rocks. As the waves retreat

the trapped air expand quickly and cancrack the rock.


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Sea Erosion

3. Abrasion this is erosion caused by smallrocks carried in the sea water hitting

against the coastline.

4. Attrition this is erosion caused by the

small stones hitting each other breakingthemselves into smaller pieces.


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Landforms of Sea Erosion

Like rivers, the sea creates many features orlandforms as a result of erosion. Theseinclude,

1. Cliffs2. Bays and Headlands3. Sea caves, sea arch, sea stack, sea stump4. Blowhole


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Cliffs

As the waves break onto the coast they cut anotch into the rock. When the notch gets deeperthe overhanging rock collapses.

This process continues and the coastline retreatsinland.

The material that falls into the sea form the cliff

is called a wave cut platform.

E.g. Cliffs of Moher, Co. Clare.


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Bays and Headlands

A bay is wide deep opening into the coastline.

A headland is a piece of land jutting out into thesea.

Bays and headlands form when there are differenttypes of rocks occur along the coastline.

The softer rocks are eroded quickly creating a bay.

The harder rocks are eroded slowly and so theystick out into the sea

E.g. Dublin Bay & Howth Head


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Bays and Headlands


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Caves, Arches, Stacks & Blowholes


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Sea Cave

A sea cave is a tunnel or passage at thebase of a cliff.

The waves erode a weak point (soft rockor an area with cracks/joints) in the cliffs.This forms a passage called a cave.


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Sea Arch

A sea arch is a passage that runscompletely through the headland.

This can happen when a cave is erodeddeep into headland, or if two caves oneither side of the headland are eroded and

join up to form a complete passage.


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Sea Stack and sea stumps

A sea stack is a pillar of rock standing inthe water near the coast.

When sea arches are eroded further theybecome wider.

Their roof collapses leaving a piece of landisolated from the coast.

This is a sea stack. It will be furthereroded by the sea to form a sea stump.


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Blowhole

A blowhole is a passage from a cave up to thesurface of a cliff top.

Compress air is trapped in the cave by strong

waves. The pressure created cracks and loosens rock in

the roof of the cave. This rock collapses overtime forming a passageway called a blowhole.

Sea spray spurts out of the opening duringstormy weather.

E.g. The Two Pistols, Co. Donegal.


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Caves, Arches, Stacks & Blowholes


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Transport by the Sea

We have already learned that riverstransport material (sand, silt, clay). This is

called the rivers load.

The sea also has a load which it transports

along. The load is made up of sand,pebbles, stones, and mud.


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Transport by the Sea

Waves are responsible for transporting theload. They do this in two ways.

1. Up and down the shore by the Swashand the Backwash.

2. Along the shore by a process known asLongshore Drift.


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Swash and Backwash

We have already looked at the processesof swash and backwash.

The swash will transport material up ontothe beach.

The backwash will transport material backdown the beach towards the sea.


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Longshore Drift

Longshore drift moves material along the beach. This occurs when waves approach the beach at

an angle.

The swash brings material up onto the beach,then the backwash brings it back down to thesea in a straight line. The swash, again movingin at an angle will move the material furtheracross the beach.

This process continues and the load is movedalong in a zig zag pattern.


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Deposition by the Sea

The sea deposits (drops off) some of itsload in sheltered places where the waves

have less energy. This may occur in a bay, or very gently

sloping shoreline.

Like river deposition which we havealready studied, sea deposition alsocreates features or landforms.


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Landforms of Sea Deposition

Sea deposition creates the following featuresalong our coastlines.

1. Beaches2. Sand Dunes3. Sand spits4. Tombolo5. Lagoons


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Beaches


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Beach A beach is made of sand and shingle (small stones) which

are deposited by the waves. The swash carries material up onto the beach. Some of

this material, especially the heavier material, stays on thebeach because the weak backwash cannot carry it back to

the sea. The backwash carries only lighter sand particlesback down towards the beach. For this reason we say that beach material is sorted, with

the heavier materials furthest from the water, and thelighter sand close to the water.

During storms, when the swash is very powerful, it canforce heavy stones high up onto the beach where theyremain to form a storm beach.

E.g. sandy beach, Curracloe, Co. Wexford.


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Sand Dunes

Sand dunes are hills of sand which formabove the high tide level.

Wind dries sand on the beach making itlighter. The sand is then blown inland untilit is trapped by a wall or vegetation.

The sand builds up to form hills of sand

which are sand dunes. E.g. Portmarnock, Co. Dublin.


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Spits, Bars, Tombolo, Lagoon


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Sand Spit

A sand spit is a ridge of sand or shingle whichextends out into the sea. It is connected to theland at one end.

Longshore drift moves material along the beach.When it reaches a shallow bay the waves haveless energy and they deposit some of the loadon the sea bed.

This material builds up over time and rise abovethe sea water.

E.g. Tramore, Co. Waterford.


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Tombolo

A tombolo is a ridge of sand or shinglewhich connects an island to the coastline.

A tombolo is formed when a sand spitoccurs linking an island to the coastlinerather than stretching across a bay.

E.g. At Howth, Co. Dublin.


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Lagoon

A lagoon is a body of water cut off from the seaby a sand spit.

When a sand spit is formed it stretches outacross a bay. It may eventually reach the otherside of the bay closing off the water behind it.

This water forms a saltwater lake called a

lagoon. E.g. Lough Gill, Co. Kerry.


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Spits, Bars, Tombolo, Lagoon


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People and Coastlines

The sea plays an important part in ourlives. Many people live by the coast, and

most of the worlds largest cities are incoastal regions.

The sea provides us with energy (oil, gas,

wave power) as well as leisure activities,transport routes, and food.


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However, the sea can also be destructive.People have tried to control this

destructive power of the sea using,

1. Sea Walls

2. Boulders 3. Groynes


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Sea Walls Sea walls are concrete walls with acurved top on them which helps to deflect thewaves back out to sea.

Boulders Large rocks are placed at the base ofcliffs or in front of sand dunes. It prevents erosionby reducing the power of the waves.

Groynes

Groynes are low walls built of wood.They are built at right angles to the shore to helpprevent sand being moved along the beach byLongshore Drift.


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Protecting the Coastline using Groynes


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Protecting the Coastline using Boulders


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Tourism and our Coastline


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Coastal land forms.ppt

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