Higher Coasts Lithosphere

Higher Coasts Lithosphere

Higher Coastal Landforms & Processes

In this part of the course we will be looking at both:coastal erosion and deposition.

Coastal Erosion

We will be looking at the following:

1)Waves our agent of erosion2) Different types of erosion3) Landforms of erosion

Coastal Deposition

We will be looking at: a. Beach profiles (X sections) & WaveTypes b. Longshore Drift c. Landforms of deposition

Coastal ErosionTo start, we must recognise that waves are responsible for coastal

erosion and that generally the bigger the wave, and the more

frequent, the greater the erosion.This means that we will need to look at how waves form and differ in size. To do this we will look at Task 1 in your work

book.

Fetch = Distance + Wind

Fetch = Distance + Wind

Coastal Erosion

Now for Task 2 all about waves actually

breaking down rock, or erosion.

Crashing Waves Erode Land

Wave Erosion

There are 3 ways that waves erode the coast. It is very important to

describe and explain these as that will get you easy marks in an exam. You’ll

need to show how they contribute towards the development of coastally eroded landforms. Watch the slides to

find out more.

The Three Main Types Of Erosion

Hydraulic Pressure

Breaking Wave

Crack In

Rock

Air Compressed

By Water

Hydraulic Pressure

Air explodes

out of crack

Over time rock

weakens and breaks

off cliff

Hydraulic PressureKey words to describe hydraulic pressure.breaking waves ~ cliff ~ water ~

cracks compresses air ~ air explodes ~ rock ~ time ~ breaks ~ force of water pounding ~ erodes ~ time

CorrasionWaves carry rocks,

shingle, sand

Rocks hit each

other

Rocks erode over

time

Corrasion (abrasive)Key words to describe corrasion.

broken rock ~ picked ~ waves thrown ~ cliff faces ~ hard rock -

erode ~ time

Attrition

Small rocks rub

against cliff

Waves carry rocks

AttritionKey words to describe attrition.

small rocks ~ H.P. ~ Corrasion waves ~ rub ~ cliff ~ erosion

Corrosion A Fourth Type Of Erosion

This is when the rock is broken down by chemicals in the sea such

as salt. Rocks can either dissolve or rot and so start to crumble away.

This is similar to solution in Limestone areas or the corrosion of

stone carried in rivers.

Landforms Of Coastal Erosion

We shall look at three principal types of landforms:i.  Cliffs/Wave Cut Platformsii. Headlands/Baysiii.Headland Erosion (On Sides)

sea cliff erosion

wave cut

platform

Sea Cliff ErosionWave Cut Platforms

(Task 3)

Sea Cliff ErosionCracks In rock are

weak points

These are eroded by waves at

high tides by the 4

processes we’ve looked

Sea Cliff Erosion

cracks get larger & form a cave

undercutting of cliff by

cave

collapse of

overhang

Sea Cliff Erosion

Repeated collapse

over time

flat terrace remnant of base of cliff

Sea Cliff Erosion

Now do Task 3 Question 1 by filling in the key

Wave Cut Platform

for later

W.C.P. exposed at low tide, but

created at high tide

Task 3 Question 21)Waves ~ erosion ~ 4 types ~

name ~ general effect ~ high tide2) Cracks ~ weak ~ widen ~ wave cut notch ~ cave ~ time ~ overhang ~ collapse of cliff (why) ~ repeats ~ retreats

3)Base of cliff ~ flat terrace ~ name it ~ exposed low tide

Headlands & Bays Task 4large headland

small headland

large bay

small bay

Headlands & Bays

two types

concordant parallel

to sea

discordant at 90º to

sea

Concordant Headlandscrack in rock

eroded by wavessoft rock

hard rock

hard rock resists waves so narrow crack

Concordant Headlands

Bay

Headland

soft rock erodes easily so wide bay

Discordant Headlandssoft rock hard rock

softer rocks erode more easily than harder ones ~ differential erosion

Discordant Headlands

bay

headland

indents or bays form on the coast where the soft rock has receded

Task Question 3

1)Geology ~ 2 key factors ~ (1) different rock types ~ hard ~ soft ~ side by side ~ (2) Layers 90º ~ sea

2)Waves erode ~ hard rock ~ slow ~ resistant ~ soft rock ~ fast ~ soft indents ~ bays hard rock ~ sticks out ~ headlands

Headland Erosion (On Sides)

These are a series of landforms

developing one after the other on

the side of a headland.

Caves/Blowholes/Arches/StacksLabel the sketch below in your work book using the word box for task 7.

Caves/Blowholes/Arches/Stacks

cavewave cut platform

blowhole

arch

stack needle

Caves/Blowholes/Arches/Stacks 1erosion

on side of headland

waves erode cracks into

caves

Caves/Blowholes/Arches/Stacks 1 Cont.

name your 3 types of erosion in exam

Explain sedimentar

y rocks easily

exploited many cracks

Caves/Blowholes/Arches/Stacks 2blowhole in

top of headland

waves crash into back of cave and erode upwards into headland

Caves/Blowholes/Arches/Stacks 2 Cont.

blowholes are relatively rare

vertical cracks in rock help them to

form

Blowhole

Roof collapses due to erosion

from waves splashing

upwards from back of cave

Caves/Blowholes/Arches/Stacks 3

continued erosion of back of cave

eventual break through to other side

forms an arch

Caves/Blowholes/Arches/Stacks 3 Cont.

process can be sped up if cracks on other side being eroded

Caves/Blowholes/Arches/Stacks 4

further erosion sees widening of arch

little support so eventual collapse

of roof

Caves/Blowholes/Arches/Stacks 4 Cont.

process can be aided by blowhole weakening roof

Caves/Blowholes/Arches/Stacks

Now try and piece together the explanations for all of these landforms Task 7 question 2

Caves/Blowholes/Arches/Stacks

1) Waves crash into headlands eroding weaker parts such as cracks.

2) The cracks are eroded by 3 different processes:- hydraulic pressure, corrasion & attrition. In an exam you should explain each of these! 3) The crack starts to widen and form a cave, it can be undercut causing the roof to collapse due to lack of support for the roof. This helps the cave get larger.

Caves/Blowholes/Arches/Stacks

4) As the cave gets larger, waves start to hit into its back wall and on impact are sent crashing into the roof of the cave where erosion occurs.

5)The erosion of the cave roof can lead to a blowhole, where waves continue to erode upwards and through the

top of the headland. This is quite rare and needs a vertical crack line to be exploited (Sedimentary Rocks!).

Caves/Blowholes/Arches/Stacks

6) At the same time caves and blowholes develop, wave

erosion can also lead to the development of an arch. This is when the cave erodes all the way through to the other side of the headland. 7) There may be similar cracks on the other side of the headland with erosion taking place, speeding up the development of the arch. Arches don’t necessary need blow holes to be present when they develop!

Caves/Blowholes/Arches/Stacks8) Over time the waves continue to widen the walls of the arch leaving less support for the roof, leading to its collapse.

This leaves a new headland on the landward side of the arch and the old wall still standing on the seaward side. 9) this old wall is called a stack or a pillar and is also subject to erosion by the sea. As it erodes it gets thinner at its base and parts of it collapse leaving a narrower pillar called a needle.

Coastal DepositionThis is essentially all about

beaches and why they develop. We will look at:

1)Swash & Backwash2)Beach Profiles3)Beach Angle & Wave Type4)Longshore Drift5)Landfroms Of Deposition

Why Beaches DevelopBeaches develop where

material is deposited due to:

1)Sheltered areas reducing wave velocity

2)A large supply of sediment from eroded features

3)Longshore Drift maintaining a beach

Swash & Backwash

swash

backwash

Swash & Backwash

water swashing

up a beach

Why Beaches Develop Swash & Backwash Task 8

Backwash

Swash

Gentle Beach Constructive Waves

circular ellipticalstrong swash

weak backwash

Gentle Beach Constructive Waves

Now for Task 9 Question 1

Complete the passage using the word box

Steep Beach Destructive Waves

strong backwash

weak swash

circular wave

elliptical wave

rotation of wave

Steep Beach Destructive Waves

Now for Task 9 Question 2 wave ~ friction ~ seabed ~

elliptical ~ just before breaking ~ steep wave

~ rotates back ~ weak swash ~

strong backwash ~ sediment lost ~

destructive wave

Longshore Drift

breaking swash breaks at angle on beach

Longshore Drift

Swash loses energy & backwash returns straight down beach due to

gravity

Longshore Drift

Zigzag movement of sediment with swash & backwash means

sediment moved along beach

Longshore Driftswash backwas

h

direction of longshore drift moving

sediment

Longshore DriftExplaining longshore drift Task 10

swash angle ~ energy loss ~ backwash ~ gravity ~ straight down ~ carries sediment ~ up ~ down ~ along beach

Landforms Of Coastal Deposition

We will look at three main landforms other than

standard beaches:

1)Spits2)Bars3)Tombolos

Spit Photograph

Spit

Longshore Drift

Spit bay

longshore drift

Spitspit

bay

longshore drift

Spit help

Bar Photograph

BarLagoon

Longshore Drift

Bars Bay

longshore drift

Bars lagoon

longshore drift

bar

Bar help

Tombolo PhotographIsland

Tombolo

Longshore Drift

Tombolo

island

bay

longshore drift

Tombolo

island

bay

tombolo

spit

Tombolo help