EARTH SURFACE PROCESSES
MODULE GEOL1003/2010/CWEM - Dr. R. Watkins
GLACIERS AND GLACIATION - OBJECTIVES
WEEKS 6&7: OBJECTIVES
By the end of this set of lectures the student should be able to:
Argue that a knowledge of glacial processes and products is important for
geologists, engineers and environmental scientists.
Define a glacier.
Describe the conditions that promote glacier formation.
With a knowledge of these conditions, predict the worldwide distribution of
major glaciers.
Identify the changes involved as snow turns to glacier ice.
Classify different types of glacier according to morphology or size
Explain how a glacier moves and describe the processes by which a glacier
erodes its bedrock.
Distinguish between a cold-based and a warm-based glacier
Describe the landforms produced by glacier erosion.
Identify the problems associated with engineering in glaciated terrain.
Give local examples of glacial landforms.
Explain what is meant by the terms - subglacial, englacial and supraglacial with respect to sediment transport
Compare and contrast ablation till, lodgement till and fluvioglacial deposits.
Describe the landforms associated with glacial and fluvioglacial deposition.
Explain why fluvioglacial sediments are an important resource and describe
what they can be used for.
Define the term ‘Quaternary’
Explain the difference between a Glacial and Stadial, and an Interglacial and
Interstadial.
Describe the fluctuations in world climate over the last 2 million years.
GLACIERS AND GLACIATION
INTRODUCTION
During the past 2 million years (a geological time period we call the QUATERNARY) there
have been many ice ages in the Northern Hemisphere. The Quaternary can be divided into:a) GLACIALS
b) INTERGLACIALS
The last major ice age in Scotland ended about 14 000 years BP - (The LATE DEVENSIAN
Ice age) and was responsible for creating the magnificent scenery of the Scottish Highlands
and Islands - For example around the area of Glen Coe, the Cairgorms, and Torridon. So
that we can interpret and develop the landscape it is necessary to understand the processes
that were once active within it. We can do this by looking at a modern analogue - i.e. we can
study present day examples and then use these as models for the past.
We can do this using the PRINCIPLE OF UNIFORMITARIANISM
Why is it important for environmental scientist, geologists and engineers to understand the
development of a glaciated landscape?
WHAT IS A GLACIER?
GLACIER -
There are sometimes permanent ice and snow patches on Ben Nevis. Could these be
considered to be glaciers?
CONDITIONS FOR GLACIER FORMATION AND GLACIER DISTRIBUTION
The conditions needed for glacier formation are:
Temperature? Precipitation? -
These conditions are satisfied at:
Which latitudes? Which altitudes? Examples?
Do we get glaciers forming in Scotland at the present day? Explain your answer.
GLACIER FORMATION
Glaciers form due to an accumulation of porous snow that gradually changes to ice in a
number of stages. First the snow will gradually compact under its own weight as more snow
accumulates on top. There is then alternate melting of the snow with the water percolating
down through the patch followed by refreezing. When most of the air has been expelled and
the snow is half way to being ice, the snow is then called?
Eventually there has been complete recrystallisation and all the air has been expelled. We
now have dense glacier ice.
What happens to the density of the snow as it turns to ice?
What happens to the porosity of the snow as it becomes more compacted?
Could ice be considered as a geological mineral?
Snow is added in the ZONE OF?
Snow melts in the ZONE OF?
The line dividing these two zones is known as the?
The end of the glacier is known as the?
The equilibrium line is not static but constantly changes. There is a significant change
between the summer and winter seasons.
What factors will control the position of the equilibrium line?
Consider a complete glacier - will the entire glacier be made of glacier ice or will some parts
be composed of snow? Explain your answer.
GLACIER CLASSIFICATION
Glaciers can be classified according to shape. There are 7 main types:
CIRQUE glacier
VALLEY glacier
FJORD glacier
PIEDMONT glacier
ICE CAP
ICE SHEET
ICE SHELF
Which glaciers have shapes that are determined by the landscape topography?
Can the Arctic ice mass (at the North Pole) be classified as a glacier?
GLACIER MOVEMENT
The ice at the surface of a glacier tends to be brittle and cracks easily. Within the glacier the
ice is under pressure and behaves more like a plastic material. Some glaciers have a layer of
water at their base due to pressure melting under the weight of the ice. These are called
WARM-BASED glaciers. Glaciers that are frozen to their bedrock are called COLD-BASED
glaciers.
A glacier can move in three different ways
a) INTERNAL DEFORMATION/CREEP
b) BRITTLE FRACTURE
c) BASAL SLIDING
The rate of glacier movement (its velocity) is not even. The centre of the ice moves at a
different rate compared to the base and sides of the ice.
Why do you think that the glacier moves at different rates?
Which part of the glacier do you think moves the fastest and how could you prove this?
Explain your answer.
Do you think basal sliding is more important in warm-based or cold-based glaciers?
GLACIER EROSION
Imagine you have two ice cubes. One is pure ice and the second one has a layer of sand
frozen into the base. If you were to rub both ice cubes over your hand which would scratch
your skin the most? From the results of this simple experiment do you think that a pure ice
glacier is as effective at eroding its bedrock compared with a glacier that has rocks embedded
in the basal ice?
Glaciers can erode by two means:
a - ABRASION
Produces Striated boulders
Grooves
Rock Flour
b- PLUCKING
Material eroded at the base of a glacier is often moved into the centre of the glacier by
internal faulting of the ice. Material on the top of the glacier is often buried under new snow
and is no longer exposed at the surface.
Do you think abrasion is more important in warm-based or cold-based glaciers?
Do you think that plucking is more important in warm-based or cold-based glaciers?
Will glacier erosion be more effective in upland areas or lowland areas?
GLACIER EROSION AND LANDSCAPE DEVELOPMENT
We have already seen that Scotland was once glaciated and the Scottish Highlands are an
excellent example of a glaciated landscape. We will now study the effects of glacial erosion
and the landscape features that are commonly exposed once the ice has retreated.
Common landscape features produced by glacial erosion
a) cirque (corrie/cwm)
b) arete
c) pyramidal peak
d) glacial valley
e) truncated spurs
f) hanging valley
g) overdeepened basin (and subsequent infill)
h) roche moutonee
i) crag and tail
j) striations and grooves
Give local examples of the above features?
Which of the above features could you use to determine the direction in which a former
glacier was moving?
What problems might there be if you wanted to construct a road through a glacial valley?
What problems might there be if you wanted to construct a dam in a glaciated valley?
GLACIER TRANSPORT
Glaciers transport large quantities of material. The glacier itself erodes large quantities of
material at the base and sides of ice and this material is then transported further down the
valley. The valley sides above the level of the ice are often unstable and landslides in this
area are common. The landslides also supply large quantities of material to the surface of the
glacier. Sometimes the glacier is so covered with accumulated debris that you cannot see the
ice underneath. This is called a dirty glacier and would normally occur in the lower reaches of
the valley where the ice is beginning to melt and sediment is accumulating.
Sediments can also be carried by the meltwater of the glacier. Meltwater can run over the
surface of the ice, actually within the ice in tunnels and underneath the ice. This water flows
towards the snout of the glacier and emerges as rivers over a floodplain in front of the glacier.
Water can also accumulate on the top of the ice and form small lakes.
Both ice and water can therefore carry eroded material.
Material can be carried:
a) SUBGLACIALLY
b) ENGLACIALLY
c) SUPRAGLACIALLY
Will the deposition of glacial material take place in upland or lowland areas?
GLACIAL DEPOSITION
Will deposition take place in the zone of accumulation or the zone of ablation?
The common terms for material deposited by a glacier is GLACIAL TILL, BOULDER CLAY
or GLACIAL MORAINE.
It is preferable to use the term TILL when referring to material that has been deposited by ice
(without the intervention of water). Material deposited by meltwater is called
FLUVIOGLACIAL SEDIMENTS.
a) GLACIAL TILL
i) LODGEMENT TILL - This is material that is deposited at the base of the glacier as the ice
is advancing forwards. It has the following characteristics:
DRUMLINS are often formed from lodgement till but may have a rock core.
ii) ABLATION TILL - is material that is deposited as the ice melts. The majority of the
material is therefore deposited from the front or the surface of the ice. It has the following
characteristics:
These landforms are characteristically formed from ablation till or are deposited when the ice
melts
LATERAL MORAINE
MEDIAL MORAINE
TERMINAL MORAINE
RECESSIONAL MORAINE
HUMMOCKY MORAINE
ERRATIC BLOCK
b) FLUVIOGLACIAL MATERIAL
This is deposited directly from the meltwater. The sediments can be deposited in front of the
glacier as the water flows out from the snout. This area is called an OUTWASH PLAIN.
Melt water can also deposit sediment within the ice and on the ice. These sediments are left
behind when the ice melts.
Under the ice if a water tunnel gets blocked with sediment - ESKER
At the sides of a glacier, where lakes often form - KAME TERRACE
Within the ice when a subglacial tunnel get blocked - KAME
Kettlehole
The characteristics of fluvioglacial material are:
Compare and contrast the sediments that are transported and deposited directly from ice to
those that are transported and deposited by meltwater. Consider the sorting and sphericity of
the sediment and the size of the sediment.
What channel patterns will the meltwater forms as it flows from the glacier snout?
What depositional landforms could you use to indicate the direction of movement of a former
ice sheet? Draw some simple sketches showing how you would use them.
In what areas of Scotland are you likely to find glacial deposits?
What problems might there be if you wanted to know depth to bedrock and were putting down
a limited number of boreholes in an area that is covered with glacial till?
If you wanted to extract gravel for road construction would you be better looking for an area of
glacial till or an area of fluvioglacial material?
What kind of extraction techniques could you use to take out the gravel?
Would you have to process the material by crushing? Would the material need washing to get
rid of fine material?
Would this be cheaper than extracting solid rock to use an aggregate?
INDEPENDENT STUDY - GLACIERS AND GLACIATION
1) READING - Please read the following text
Press and Siever - Understanding Earth, Chapter 15, pages 329-345 and page 390
2) REVIEW THE VIDEO - GLACIERS AND GLACIATION
You can review this video in F115. Please see David Wallace (The geology technician) when
you want the video setting up. It is better if a group of you organise to go at the same time.
3) Make sure that you can define or describe all of the terms that are highlighted in bold
within the lecture notes.
4) Check that you have answered all of the questions within the lecture notes (they are also
listed at the end of the notes). Answers will be on BLACKBOARD.
5) For revision, please attempt the self-assessment questions and check that you can
achieve the lecture objectives.
Useful web sites
http://www.casdn.neu.edu/~geology/department/staff/colgan/iceland/glaciers.htm (Notes)
http://www.geo.duke.edu/geo41/gla.htm (Photographs)
http://www.tulane.edu/~sanelson/geol111/glaciers.htm (notes)
If you need any help, please see a lecturer as soon as possible.
QUESTION FROM LECTURE NOTES (these are the questions that have appeared in the
lecture notes, please make sure that you can answer them). You will need to refer to your
textbooks.
1. Why is it important for environmental scientists, geologists and engineers to understand
the development of a glaciated landscape?
2. Some years there is permanent snow near the top of Ben Nevis. Could this be classified
as a glacier?
3. Do we get glaciers in Scotland at the present day? Explain your answer.
4. What happens to the density of snow as it turns to ice?
5. What happens to the porosity of snow as it becomes more compacted?
6. Could ice be considered a geological mineral?
7. What is the equilibrium line?
8. What factors control the position of the equilibrium line?
9. Is a glacier completely made of glacier ice or are some parts composed of snow? Explain
your answer.
10. Why do different areas of a glacier move at different rates?
11. Which part of the glacier moves fastest and why? How could you test for this?
12. Do you think that basal sliding will be more important in a warm-based glacier or a coldbased glacier?
13. Compare and contrast the sediments that are transported and deposited directly from ice
to those that are transported and deposited by meltwater. Consider the sorting and
sphericity of the sediment and the size of the sediment.
14. What channel patterns will the meltwater forms as it flows from the glacier snout?
15. What depositional landforms could you use to indicate the direction of movement of a
former ice sheet? Draw some simple sketches showing how you would use them.
16. In what areas of Scotland are you likely to find glacial deposits?
17. What problems might there be if you wanted to know depth to bedrock and were putting
down a limited number of boreholes in an area that is covered with glacial till?
18. If you wanted to extract gravel for road construction would you be better looking for an
area of glacial till or an area of fluvioglacial material?
19. What kind of extraction techniques could you use to take out the gravel?
20. Would you have to process the material by crushing? Would the material need washing to
get rid of fine material? Would this be cheaper than extracting solid rock to use an
aggregate?
SELF-ASSSEMSSMENT QUESTIONS
1. What is the ‘Quaternary’?
2. What is the Principle of Uniformitarianism?
3. Why is the Principle of Uniformitarianism important to geologists?
4. What is a glacier?
5. What are a glacial and an interglacial?
6. What conditions are suitable for glacier formation?
7. Where can you find glaciers on the Equator?
8. What is the zone of ablation?
9. What is the zone of accumulation?
10. Describe the three ways in which glacier ice can move.
11. What are the difference between a warm-based and a cold-based glacier?
12. Distinguish between the different types of glacier – Cirque, Valley, Fjord,
Piedmont, Ice cap, Ice sheet, and Ice shelf and explain how they are classified.
13. Describe the landforms that result from glacier erosion.
14. Compare and contrast ablation till, lodgement till and fluvioglacial deposits.
15. Explain how the following are formed and describe how you would recognise
them as a landscape feature:
Lateral moraine
Medial moraine
Terminal moraine
Recessional moraine
Hummocky moraine
Erratic block
16. What is an outwash plain
17. What is an esker and how does it form?
18. What is the difference between an esker and a lateral moraine?
19. What is a kame terrace and how would one form?
20. Explain why fluvioglacial sediments are an important resource?
EARTH SURFACE
PROCESSES
GLACIATION
AND
GLACIAL
DEPOSITS