Glaciation

Question 1

What is a glacier?

Answer 1

A glacier is a large body of ice which moves down a valley (which is usually sheltered from the sun) which it has mostly carved out itself.

Question 2

How do glaciers form?

Answer 2

• Glaciers form when snow and ice do not completely melt before next years snowfall.
• This usually occurs in shaded areas between tall peaks at high altitudes where it is cooler.
• As the depth and weight increases, the bottom layers compress and crystallise.

Question 3

What is moraine?

Answer 3

Lines can appear when two glaciers come together, causing transported material called moraine on the sides of the glaciers to merge between the two.

Question 4

What are accumulation / ablation?

Answer 4

Accumulation:

• A zone where a glacier gains ice.

Ablation:

• A zone where a glacier loses ice.

Question 5

How does a glacier move?

Answer 5

1. At the top of a mountain, temperatures are cold and so snow accumulates, getting deeper and deeper.
2. This adds weight to the glacier causing it to eventually slide downhill.
3. As it gets lower, the temperature increases, and so ablation occurs through:

• Sublimation = when a solid turns to gas.
• Icebergs = if a glacier runs into a lake, icebergs break off into the lake.
• Melting = can occur if temperatures are very high.

Question 6

What causes a glacier to move faster?

Answer 6

1. Once a glacier is thick enough, the heat from the core of the Earth as well as the increased pressure from the extra weight causes the base of the ice to melt.
2. This forms a layer of liquid water, causing the glacier to move very quickly.

Question 7

What type of flow does a glacier have?

Answer 7

Plastic Flow:

• Shear stresses within the glacier cause the ice crystals to change shape, producing gentle flow through the shear deformation of ice.

Question 8

What are the differences between warm and cold based glaciers?

Answer 8

Warm (water) based:

• The whole glacier will slide in a basal slip because the shear strength is low at the base.

Cold (frozen) based:

• The glacier cracks and folds as the base is frozen to the ground meaning the particles at the bottom do not move.

Question 9

How can you tell if a glacier is advancing/retreating?

Answer 9

Advancing glacier:

• The ground ‘in front’ of the glacier will have vegetation on it.
• The ‘front’ of the glacier will be very steep and jagged.

Retreating glacier:

• The ground ‘in front’ of the glacier will be made up of exposed moraine material.
• The ‘front’ of the glacier is a gentle slope.
• Overall the glacier is moving downwards but is being dominated by melting.

Question 10

What is an ice cap?

Answer 10

1. An ice cap is a glacier where so much snow and ice accumulate that the weight of it pushes downwards on the continental crust.
2. Eventually, when the snow and ice melt, this continental crust fills with water.
3. After this, an isostatic rebound will occur where the continental crust rises again to become exposed ground surface.

Question 11

What are the types of moraine?

Answer 11

End moraine:

• Found at the ice front.

Terminal moraine:

• Found at the ice front marking the farthest advance of ice.

Lateral moraine:

• Found along the edge of a glacier where it scrapes the side walls of the valley.

Medial moraine:

• Found when two glaciers merge, joining their lateral moraine.

Ground moraine:

• Found beneath the ice as a layer of glacial debris.

Question 12

What are striations?

Answer 12

Lines produced when accumulated rocks (that are being driven along by the ice that they are frozen into) gouge a groove into the rocks that a glacier moves over.

Question 13

What types of valley do glaciers produce?

Answer 13

Glaciers erode around their whole perimeter meaning very large u-shaped valleys are produced.

Question 14

How are crevices formed?

Answer 14

When a glacier moves around corners or over bumps, they change direction, forming deep cracks called crevices.

Question 15

What happens when a glacier moves over a drop?

Answer 15

Lots of moraine is deposited at the bottom of the drop, leading to an accumulation of different sediments.

Question 16

How is end moraine deposited?

Answer 16

It is deposited at the end of a glacier where the stream doesn’t have enough energy to transport materials.

Question 17

What is a drift?

Answer 17

The material left at the front of a glacier.

Question 18

What is outwash?

Answer 18

Material which is transported by the melted ice.

Question 19

What are the features of a post-glacial landscape?

Answer 19

1. V-shaped valleys are generated by rivers, typically producing rounded mountain profiles.
2. The glaciers then fill the whole of these valleys, scouring out the entire valley side, producing a U-shaped valley.
3. Tributary glaciers join the main glacier meaning erosion comes to a halt, producing a hanging valley with a waterfall somewhere up the side of the main valley.
4. This waterfall then gradually cuts a V-shaped valley into the tributary U-shape valley.
5. This forms sharp aretes between two adjacent glaciers.

Question 20

What are fjords?

Answer 20

A fjord is an in-field depression where a glacier has previously been eroding away.

1. Ice bergs which have been carved off of the glacier float away and continue to erode the valley deeper and deeper.
2. However, once they reach the sea, erosion stops and so the fjords are much deeper than the sea itself.

• If the sea level falls, land locked lakes are formed.

Question 21

How can a series of lakes be produced?

Answer 21

A series of lakes may be produced in the bottom of a U-valley where bands of end-moraine result in damming of the valley.

Question 22

Quick Clay, The Rissa Landslide, Norway (Case study)

Answer 22

1. Deposits of marine clay were built upon on a farm in Norway.
2. The earth removed to build a basement was placed on the edge of the fjord.
3. The load produced by this earth fill caused the shoreline to slide into the lake and disappear.
4. Each new slide resulted in a complete liquefaction of the quick clay.

Question 23

What are the effects of an ice sheet?

Answer 23

If an entire area is covered by an ice sheet, everything gets smoothed over by the ice of the glacier and so the hills are small and rounded.

Question 24

How are braided meltwater streams produced?

Answer 24

Streams below the glaciers carry lots of sediment which is deposited to form a pattern of water flow.

Question 25

How are kettle holes produced?

Answer 25

Kettle holes are left where large blocks of ice have prevented deposition from taking place, resulting in lakes or underground voids being produced.

Question 26

How are drumlins produced?

Answer 26

Drumlins are small mounds produced of moraine which has been streamlined by the ice moving over it.

Question 27

How are eskers produced?

Answer 27

Eskers are a meandering ridge of sand and gravel which is deposited at the bed of a river which previously flowed underneath a glacier.

Question 28

How is boulder clay / glacial tills formed?

Answer 28

Boulder clay is made up of a wide range of particle sizes with lots of angular pieces, that are deposited by the melting ice.

Question 29

What affects do glaciers have on stones?

Answer 29

Stones are transported and deposited by melting ice, meaning sometimes they do not bear any reflection to the rocks around them.

Question 30

How is a varve produced?

Answer 30

When a lake is frozen solid, only the fine particles can settle into the bottom of the lake. However, when thawing occurs in spring, fine particles are transported, leaving only courses particles to be deposited. This produces a sequence of differently sized deposits on the bed of a lake. This allows you to age each sediment layer.

Question 31

Why does the amount of ice on Earth’s surface vary?

Answer 31

The amount of ice varies periodically at interfering frequencies due to the eccentricity, precession and tilt of the Earth.

Question 32

How does eccentricity effect the Earth?

Answer 32

• If the eccentricity is high, the Earth will be significantly further away from the sun at certain times of years compared to others.
• If this point coincides with winter, you will get a colder winter.
• Low eccentricity produces less variation between summer temperature and winter temperatures.

Question 33

How does tilt effect the Earth?

Answer 33

The hemisphere tilted towards the sun gains more heat. At the North Pole, there is only sea and so water just freezes and melts every winter and summer. At the South Pole, there is continental crust which allows the build up of large volumes of ice. As the tilt gets greater, the intensity between summer and winter is increased.

Question 34

How does precession effect the Earth?

Answer 34

• The direction which the Earth’s axis is tilted wobbles in a process known as precession.
• This means that the tilt of the Earth will interfere differently with the changes in eccentricity.

Question 35

How does the golf stream effect the Earth?

Answer 35

• Water is in ocean circulation, resulting in some shallow, warm currents known as the Gulf Stream.
• These circulations change easily meaning different areas will experience different temperatures at different times.

Question 36

How did the Earth exit it’s ‘snowball’ stage?

Answer 36

1. Glacial dropstones were identified, showing that at some point the Earth was covered in ice which reflects a lot of heat, keeping it very cold.
2. Eventually, volcanic activity released large amounts of CO2 and ash which deposited onto the snow making it darker.
3. Therefore, more heat was absorbed and so the snow melted.