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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: Waves our agent of erosion Different types of erosion Landforms of erosion. - PowerPoint PPT Presentation
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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
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