Transcript An introduction to glaciation2x

WOW!!!
I wonder how
this valley was
formed?
An introduction to Glaciation
Key Questions:
1. What is a glacier
2. Why study them?
What is a glacier?
• A glacier is a huge mass of ice resting on land
or floating in the sea next to land, they usually
move very slowly. A glacier acts in a similar way
to an immense river of ice, often merging with
other glaciers in a stream-like manner.
• Why are glaciers worth knowing about?
Glaciers are beautiful natural features
The action of glaciers produces some very distinctive landscape
features
Pyramidal peak
arete
Fjord
Melting glaciers might bring problems for us all!
What is a glacier?
• https://www.youtube.com/watch?v=k6gk1b4
ACP0
Figure 1: How much of the British Isles was covered in ice?
The Ice Age in Britain
began about
1,000,000 years ago
and lasted until about
20,000 years ago.
During this time
temperatures
fluctuated and ice
advanced and
retreated four times.
The northern and
eastern parts of the
British Isles were
covered in ice.
Use an atlas to help you name the source regions of
the valley glaciers.
What are the main
parts of a glacier?
Find a partner…
What is a glacier?
Key terms
• Accumulation zone: area in the upper glacial valley where
new snow and ice forms.
• Ablation zone: the loss of ice from a glacier due to melting.
• Moraine: a mixture of rock and sediments left behind when a
glacier melts.
• Bergschrund: A glacial crevasse (large crack) that forms when
the glacier pulls away from the stagnant ice above.
• Tarn lake: when water collects in a depression in a glacial
valley.
• Neve: new snow/ice that collects on a glacier. Snow and ice
that survives one season becomes known as firn.
Key terms
1. _______: a mixture of rock and sediments left behind when a
glacier melts.
2. _______: A glacial crevasse (large crack) that forms when the
glacier pulls away from the stagnant ice above.
3. _______: when water collects in a depression in a glacial
valley.
4. _______: new snow/ice that collects on a glacier.
5. Snow and ice that survives one season becomes known as
______
Bergschrund: A glacial crevasse (large
crack) that forms when the glacier pulls
away from the stagnant ice above.
Bergschrund: A glacial crevasse (large crack) that forms
when the glacier pulls away from the stagnant ice above.
Tarn lake: when water collects in a
depression in a glacial valley.
Moraine: a mixture of rock and sediments
left behind when a glacier melts.
Make three annotated sketches for a tarn lake, a moraine and a bergschrund
crevasse.
Look at the two photos.
What is different about them?
Can you think what might have caused them to
be different?
Glaciers: Why are they called
Nature’s Bulldozers?
To know why glaciers are called nature’s bulldozers
To know how glaciers change the shape of the land
Formation of a glacial trough
How does ice shape the land?
• Although Glacial ice appears solid it can behave
like a fluid, when it pushes up against an object it
is solid enough to erode it but fluid enough to
move around it like water in slow motion.
• Melt-water lubricates the glacier and helps it to
slip along the valley bottom, often refreezing
around rocks and carrying them with it.
• This movement can change the shape of the
valley in which the glacier moves.
A U-shaped glacial valley
V shaped valley
formed by river
erosion
Compressed
snow
U shaped
valley
Glacier
Explain how ice
shapes the land in
no more than 20
words.
What is the
difference between
erosion and
weathering?
Erosion and weathering
• Erosion is the wearing away and removal of
material
• Weathering is the action of the weather
wearing away material in situ (where it is).
THREE images but
what links do they
have with GLACIAL
EROSION?
Glacial Weathering/Erosion
There are THREE main types of glacial erosion:
• Plucking
• Abrasion
• Freeze thaw
Task
1) Find a partner and sort yourself into the roles of TEACHER and
STUDENT.
2) The TEACHERS will be shown three statements about each erosional
pattern for 3mins only.
3) Using the knowledge recently gathered and the image the TEACHER
needs to EXPLAIN what's happening with the THREE glacial erosional
patterns (abrasion, plucking and freeze thaw) to the STUDENT.
• Freeze-thaw is a process of weathering that
happens when melt water or rain gets into
cracks in the bedrock (usually the back wall).
At night the water freezes and expands
causing a crack to get larger. Fragments may
then fall under gravity.
• Plucking is when melt water from a glacier
enters cracks in the rock. It then freezes to the
glacier and base rocks. When the ice moves
downhill, rock is plucked (pulled out) from the
back wall and carried a long by the glacier.
• Abrasion is a sandpapering action. It happens
when rocks in the base and sides of the glacier
rub against the valley floor and sides as it
moves. This wears away the rock, often
leaving them with scratches.
• Plucking is when melt water from a glacier enters
cracks in the rock. It then freezes to the glacier and
base rocks. When the ice moves downhill, rock is
plucked (pulled out) from the back wall and carried a
long by the glacier.
• Abrasion is a sandpapering action. It happens when
rocks in the base and sides of the glacier rub against
the valley floor and sides as it moves. This wears
away the rock, often leaving them with scratches.
• Freeze-thaw is a process of weathering that happens
when melt water or rain gets into cracks in the
bedrock (usually the back wall). At night the water
freezes and expands causing a crack to get larger.
Fragments may then fall under gravity.
Process
Freeze-Thaw
Diagram
Description
Make a copy of this
table on a full page of
your book, then
complete the table.
Abrasion
Plucking
Recap:
How does a glacier form?
Re-arrange the following into the correct order
A. The residual snow settles, becoming more
compact and dense.
B. The great weight of the top layers compacts the
deep layers.
C. Snow falls.
D. Annual snow accumulation far exceeds the annual
snow melt.
E. Compacted snow freezes together and creates
sheets of ice.
F. The number of layers increases.
C, D, A, F, B, E.
Processes operating in a glacial valley
• Erosion =
Breaking down of material
by the action of the weather.
• Weathering =
Movement of material from
one place to another.
• Transportation =
• Deposition =
Wearing away of the rock
and surface.
Putting down of material
somewhere else.
Freeze Thaw weathering
Arrange these into the correct order.
Draw a diagram(s) to show the process happening.
1. Eventually this continuous process causes rocks to
break up.
2. As the water freezes it expands and causes the cracks
to widen.
3. This cycle continues, each time widening the cracks.
4. During the day when the sun is out, cracks in rocks get
filled with water as the glacial ice melts.
5. The next time the temperature rises, the ice melts,
the water thaws and contracts.
6. At night the temperatures become colder and the
water in the crack freezes.
4, 6, 2, 5, 3, 1.
Abrasion is an
important process of
glacial erosion.
Describe how it occurs.
(3)
Abrasion uses material the glacier is carrying/transporting (1).
This is from the surrounding valley sides (1) as a result of
freeze thaw weathering (1)/plucking(1). The material is used to
grind the sides and floor of the valley (1) like a sandpapering
effect so that it is worn away (1).
NEED ONE OF THE FINAL 2 POINTS FOR ALL 3 MARKS.
Upland glacial features (erosion)
THE FORMATION OF CORRIES,
ARETES AND PYRAMIDAL PEAKS
Watch the video of the formation of
a corrie and afterwards describe the
formation to a partner.
Erosional features: Pyramidal peaks, aretes and
corries
http://www.youtube.com/watch?v=uYwGVVK3H2c
Now watch a second video that describes
how the formation of a corrie(s) can lead to
the formation of aretes and a pyramidal
peak. Use this information to explain the
diagrams on the next few slides.
http://www.bing.com/videos/search?q=THE+FORMATION+
OF+A+CORRIES%2c+ARETES+AND+PYRAMIDAL+PEAKS+AND
+&view=detail&mid=3FA6AD43567F6AF0C2CF3FA6AD4356
7F6AF0C2CF&first=0&FORM=NVPFVR
Task 1
• Add the names and definitions onto the worksheet:
Glacial mountain features.
Task 2
• Design a cartoon strip to show the formation of a
corrie, arete and pyramidal peak.
• Draw a simple diagram and write a short caption
underneath.
e.g. Step 1: Snow gathers on a hillside and begins to
accumulate, eventually it becomes compacted and
turns to ice.
Exam question - recap
Explain the formation of a corrie (4 marks)
A corrie is an arm chair shaped hollow on a hillside. It is formed
when snow and ice collect in a hollow.
The snow and ice move downhill under the force of gravity and
the back wall of the hollow is plucked out and steepened.
The plucked material is carried by the glacier – it rubs against the
base of the hollow and deepens it.
Ice is thinner at the front of the hollow and so there is less
erosion – this leads to the development of a rock lip.
When glaciation is over and the snow and ice melt the corrie
may fill with water forming a corrie lake (tarn lake)
The formation of a
corrie
Exam question:
Explain the formation of a
pyramidal peak 4 marks)
A corrie is a bowl shaped depression in a glaciated landscape. The are found in the upper glacial
valley.
Step 1: Snow gathers in a small hollow on a hillside – snow accumulates and eventually it becomes
compacted and turns to ice.
Step 2: When the ice is thick enough it moves out of the hollow and down the slope under the force of
gravity.
Step 3: As it moves it causes plucking at the back of the hollow – this steepens the wall of the hollow.
Step 4: The plucked material is carried by the glacier. It rubs against the bottom of the hollow making it
deeper (abrasion).
Step 5: Ice moves out of the hollow in a rotational manner – the thicker ice in the middle of the hollow
exerts a lot of pressure , giving very high rates of erosion.
Step 6: At the front of the hollow the ice is thinner and there is less erosion – this means a rock lip is
left at the front of the hollow.
Step 7: After glaciation has finished corries often fill with water – forming a corrie lake/tarn lake.
Pyramidal Peak - formed where three or more corries intersect
back to back, forming a sharp, pointed hilltop between them
Mount Snowdon
13.08.03
St Ivo School Geography Department
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Erosional features: fjords
A fjord is a long, narrow arm of the sea, often
extending well inland, that results from
marine inundation of a glaciated valley. Many
fjords are remarkably deep; the huge glaciers
that formed in these valleys were so heavy
that they eroded the bottoms of the valleys
far below sea level. After the glaciers melted,
the waters of the sea invaded the valleys.
http://www.youtube.com/watch?v=y0pvswzqCX
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Lower glacial features of erosion:
Fjords
1. What is a fjord?
2. How does it form?
Features of deposition - Moraine
Types of moraine
Material found along the edge of
a glaciated valley is called
lateral moraine.
If two glaciers meet, their lateral
moraines join together
forming medial moraine. This
leaves a line up the centre of
the valley.
A terminal moraine is a ridge of
material deposited at the
front of the glacier marking
the furthest point the glacier
reached down the valley.
Erratics
Drumlins