Transcript HIGHER GEOGRAPHY - Thurso Geog Blog

LITHOSPHERE CORE
COASTLINES
Lesley Monk
Balfron High School
Session 2005/6
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LITHOSPHERE CORE
COASTLINES
CONTENTS
Slide-show 1-Coastlines of erosion
Slide-show 2-Coastlines of deposition
Slide-show 3-Coastlines of changing sea level
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COASTLINES
MARINE EROSION
PROCESSES.
Read the course booklet, page 11.
You will need to know and be able to explain the four
methods of coastal erosion and two of weathering on
the page.
The next few slides illustrate these processes.
These slide-shows are all on the Prepwork folder if
you wish to copy any notes from them; we will not be
stopping in class for you to do this
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Hydraulic Action
COASTLINES
The force of waves
hitting a cliff (or
sea wall) compresses
water and air into
cracks and joints.
This increase in
pressure may lead to
cracks widening and
pieces of rock
breaking off.
There is no separate picture for wave pounding!
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Abrasion
COASTLINES
Rock fragments may be
picked up by waves and
thrown against the rock face
of cliffs by subsequent
waves.
Sometimes the softer strata
are abraded more than the
harder ones, giving a striped
appearance.
Abrasion is most effective
at the base of cliffs.
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Wave attrition
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Rock fragments are worn
down into smaller and
more rounded pieces.
Currents and tidal
movements cause the
fragments to be swirled
around and to grind
against each other.
This type of erosion
produces pebble
beaches.
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Water- layer weathering
Alternative wetting and
drying -as happens with
the rise and fall of the
tides -can disintegrate
porous or coarser rock
layers.
Salt crystals growing in
rock spaces can do the
same thing.
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Corrosion (solution)
Salts and acids in sea
water can react with
rocks , slowly dissolving
them away.
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TEST YOURSELF!
Match the processes with the description on
the next slide by writing them out in your
jotter. Write these ‘heads’ first, leaving a
space of about three lines for each,to write in
the tails…….
heads
Hydraulic pressure isCorrasion isAttrition isCorrosion/solution is9
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-the chemical weathering of the cliff
when salts and weak acids dissolve rock
minerals.
-the sheer force of the waves as they
crash into a cliff explode, compress the
air, and cause the face to break up.
-the sandpaper effect when waves, armed
with rocks and pebbles, rub away the
base of the cliff.
-rocks and pebbles rub against each other
on beaches forming smaller and smaller
particles.
tails
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Rates of erosion depend on many
factors: (Copy this note into your jotters. Discuss
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the factors in class.)
Waves – strength, frequency,
height
Weather – frequency of storm
conditions
Geology of the coastline :
-type of rock
-orientation of stratification
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The FETCH is the
distance travelled
by waves from one
shore to another.
The waves hitting
the southwest
coast of England
have a fetch of
about ten
thousand miles!
Copy this note!
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There are eight erosion-related features you need
to learn up.
You need to be able to ;Describe them using their proper terms
Explain IN DETAIL how they form
Draw simple LABELLED SKETCHES of them
Give EXAMPLES of them in the UK.
BAY AND
STACK
HEADLAND
NEEDLE
ARCH
ABRASION
NOTCHES
STUMP
CAVE AND
BLOWHOLE
WAVE-CUT PLATFORM
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Many erosion features are a result of rocks of
varying hardness occurring beside/below each
other. The DIFFERENTIAL EROSION between
them creates the landform.
(Note that mass movements may also be
triggered as a result. )
Read about them on pages
12-13 of the booklet, and
answer the questions to
help focus your attention
on the most important
factors.
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Q1. What two properties of a headland tell us
that the rock is hard?
A. It juts out into the sea and is high ground.
Q2. What two properties of a bay tell us that
the rock is soft?
A. It eats back into the land and is lower ground.
Q3. On a new cliff coast, what is the first
feature caused by erosion?
A. Abrasion notches are created initially.
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Q4.Cliff retreat creates which feature all along
the coast?
A. It creates a wave-cut platform.
Q5.Why is this only exposed at low tide?
A. Erosion only happens between high and low tide
marks, and no erosion takes place below LTM.
The ‘top’ of the eroded cliff is the WCP, seen
only when the tide is lowest.
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COASTLINES
Headland erosion near Noss Point
Caithness
The sea is eroding this headland back leaving a wavecut platform below the waves.
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How Are Wave Cut Platforms Formed?
(Copy this note into your jotter.)
Erosion is greatest when large waves actually break
against the foot of a cliff.
The foot of the cliff is undercut to form a wave
cut ( abrasion) notch.
As the notch gets larger the cliff above becomes
increasingly unsupported and in time collapses (
often by a mass movement process!)
As this process continues the cliff will slowly
retreat.
The flat land left at the foot of the cliff is called
a wave cut platform
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Cliffs and Wave Cut
Platforms
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There is a copy of this diagram to stick
into your jotters. Add in the labels to your
copy.
1
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Sea Inlet near Noss Point
Caused by hydraulic action at a
weakness in the rock.
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Sea Inlet At Duncansby Head
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There is a copy of this diagram to stick into your
jotters. Copy the text onto your copy of this
diagram.
Note;- for a
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cave to
occur, there
must be an
area of
weakness in
the cliff
face.
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Smoo Cave near Durness
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A Blowhole or ‘gloup’ may
form if the erosion at the
back of the cave breaks
through the roof to the top
of the cliff.
This usually happens at high
tide in stormy weather.
Copy this note!
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There is a copy of this diagram to stick into your
jotters. Copy the text onto your copy of this
diagram.
3
notches
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An arch
forms when
the sea
breaks
through to
the other
side of the
headland.
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Natural Arch
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Close up of Duncansby Stacks
and Stump
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Stack At Sandwood Bay
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MINI-HOMEWORK EXERCISE
Take a copy of the homework exercise. It is
a feature- identification and explanation
task.
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Answer it on A4 sized paper, and hand it in
for marking at the start of next lesson.
Please write it in ink or word- process it,
proof-read it, and put your name on it!
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Suggested answers -available later!
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Coves are a special feature and we will learn about
them by looking at a case study of Lulworth Cove.
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Lulworth Cove was formed by differential
erosion. The next slides will explain how this
happened.
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The geology of Lulworth Cove
hard
soft
Copy the diagram
and explanation.
The hard rock at the
coast has been
breached. The sea
can now get in to
erode the softer rock
behind, creating the
cove. The second
layer of hard rock
stops the cove
growing much larger.
You will learn the names of the rock types in the
Case Study unit- Rural Land Resources.
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Click on the hyperlink to see the video clip about
Lulworth cove.
HYPERLINK
Add to your notes to make sure that you can
answer a question about this feature in an exam.
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ORDNANCE SURVEY MAPWORK
You need to be able to recognise
coastal erosion landforms from a
map.
To practice this skill, take a copy
of the question sheet and the two
O.S. maps and tackle the questions.
THEY ARE NOT ALL EASY !!
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As you go through the next (revision)
slide, for each feature mentioned, look
back through your unit booklets and this
presentation. You are looking for named
examples of as many features as possible.
Perhaps you could work
in pairs to do this
task!
THEN PLAY THE COASTLINE DOMINOES GAME!
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You have now completed the erosion section.
You should be familiar with the following terms and be
able to define and use them in your answers. Copy this.
PROCESSES
FEATURES
SOLUTION
BLOWHOLE
ARCH
FETCH
WAVE POUNDING
NEEDLE
CAVE
STRATIFICATION
ABRASION
ATTRITION
STUMP
STACK
ROCK
ORIENTATION
HYDRAULIC
ACTION
BAY AND HEADLAND
WATER-LAYER
WEATHERING
COVE
RELATED TERMS
INLET
NOTCHES
DIFFERENTIAL
EROSION
WAVE-CUT PLATFORM
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