Glaciation

Ice Ages

• Every 200-250 million years, theEarth appears to go throughmajor periods of ice activity.

• In the past 2 million years, therehave been fluctuations in globaltemperature of up to 10°C,leading to cold phases (glacials)and warm phases (interglacials).

• By studying the ocean floor andAntarctic ice cores, scientistshave discovered that in the last750,000 years, there have been8 ice ages separated by 8interglacials.

What is an Ice Age?

• An ice age is a long period ofvery low temperature on Earth’ssurface and atmosphere.

• This results in the presence/expansion of continental andpolar ice sheets and glaciers.

What is a Glacier?

A large river of ice which moves very slowly downhill.

It forms where the accumulation of snow is more than the ablation or melting.

Example: Aletsch Glacier in Switzerland

How do Glaciers form?

A glacier behaves likes a system with inputs,flows and outputs. A glacier may take tens tohundreds of years to form.

• Inputs: precipitation from snow or avalanches.

• Flows: with continuous snow fall, the underlyinglayers are compressed and turn into ice. (Icewithout any oxygen in it turns blue forming aglacier). Once ice is formed, the glacier starts tomove downhill under the influence of gravity.

• Outputs: meltwater and evaporation.

When the inputs are less than the outputs, theglacier retreats. At present, most of the world’sglaciers are retreating.

Glacial systems

Zone of accumulation:• The upper part of the glacier

where inputs are greaterthan the outputs.

Zone of ablation:• The lower part of the glacier

where outputs are greaterthan the inputs.

Zone of equilibrium:• The zone where the rates od

accumulation and ablationare equal

Glacier budget/ net balance:

The difference between the total accumulation and the total ablation for one year.

Processes of Ice Erosion

1. Abrasion▪ When material carried by a glacier rubs against the sides and floor of the

valley causing erosion (like sand-paper).

2. Plucking▪ Glacial ice freezes onto solid rock. When the glacier starts to move, it pulls

away these large pieces of frozen rock with it.

3. Freeze-thaw weathering (frost shattering)▪ Water enters the cracks of rocks during the day and freezes during the night

as it gets colder. As the water turns into ice, it expands and puts pressure on the surrounding rock, causing pieces to break off.

Glacial features and how they form…

Basic diagram Detailed diagram

Corries

• They started to form in the beginning of the Ice Age when snow accumulated in hollows on hillsides. Freeze-thaw and plucking then led to their formation, together with abrasion which made the hollows even wider and deeper forming rock basins.

• After the Ice Age, corries acted as a natural dam to meltwater forming the more round corrie lakes.

• Corries are deep,rounded hollowswith a steep backwall and a rockbasin.

• They are alsoknown as ‘cirques’or ‘cwms’.

Examples of corrie lakes

Arêtes and pyramidal peaks

• When 2 or more corries develop back toback, they erode backwards towards eachother.

• The land between them starts to getnarrower until a ridge forms – aka – arête.

• If 3 or more corries cut back-to-back intothe same mountain, a pyramidal peakforms – aka – horn.

U-shaped Glacial Troughs

• When glaciers move downhill through valleys,their erosive power is able to widen, deepenand straighten the valley floor and its sides.

• This results in the V-shaped valley to becomemore U-shaped as a glacial trough.

U-shaped glacial troughs

Truncated Spurs

• As the glacier continues to move down the valley, itremoves the ends of interlocking spurs. In turn, thisproduces the more ‘cliff-like’ structures called –truncated spurs.

Interlockings Spurs

Hanging Valleys

Hanging valleys are located between adjacenttruncated spurs.

How do they form?

1. Before the Ice Age, tributary rivers would flowdirectly into the main river (at the same heightabove ground).

2. During the Ice Age, the main valley would havea larger glacier than the tributary valleys, so theerosion is much bigger and deeper in theground.

3. When the ice melted, the tributary valleys wereleft ‘hanging’ above the main valley where theflowing water only meets the river viawaterfall.

Ribbon Lakes

How do they form?

1. Glaciers move down a valley and start to erode it byabrasion and plucking.

2. When the glacier meets softer underlying rock, iterodes it much more deeply than the rest of therock.

3. After the glacier melts, the water fills the deeperpart and form – ribbon lakes.

Ribbon Lakes

What is Moraine?

• Moraine is material, mainly angular rock, which is transported and later deposited by a glacier.

• The deposition occurs when the temperature rises, resulting in the glacier to melt, leaving this material behind.

Types of Moraine…

1. Lateral moraine

2. Medial moraine

3. Ground moraine

4. Terminal moraine

5. Recessional moraine

Lateral moraine

Material derived from freeze-thaw weathering of valley sides and which is carried and deposited at the sides of a glacier.

Medial moraineDebris found in the center of a glacier and results from two lateral moraines joining

together.

Ground moraine

Material dragged underneath a glacier forming a flat valley floor once it is

deposited.

It is also known as – till or boulder clay.

Terminal moraine

This marks the maximum advance of a glacier.

It is material deposited at the snout (end) of a glacier.

The longer the glacier the remains in the same place, the larger the terminal moraine.

Recessional moraine

This is material which is deposited behind, and parallel to the terminal moraine.

This marks interruptions in the retreat of a glacier when it remained in the same

place for long enough, allowing further ridges to form across the valley.

Terminal and recessional moraine can act as natural dams behind which ribbon

lakes can form.

Recessional moraine

Features of glacial deposition

Erratics:▪ Rocks and boulders carried by ice and deposited in an

area of totally different rock.

Drumlins:▪ Hills of sediment formed parallel to the direction of ice

movement. Mostly stones and clay.

▪ They result from the deposition of a heavy load being carried by the glacier. (it would have been too heavy to continue carrying so it was deposited).

Erratics

Drumlins

Land use in glacial areas

1. Farming

2. Forestry

3. Water supply

4. HEP

5. Tourism

Glacial highlands and human activity…

Apart from being scenically attractive, glacialhighlands provide a variety of opportunities fordifferent human activities.

These areas often have most of their soilremoved by the glaciers, have steep slopes anda cold-wet climate.

However, human activity can pose severaldangers in terms of ruining the natural beautyof glaciated areas.

Farming

Glacial highlands tend to be ideal for sheep farming.

In some countries such as Norway and Switzerland, farming in these areas involves a seasonal movement of animals – depending on the presence of grasslands.

(See also pg 100 from the book)

Forestry

In areas where the land is not too steep and has some soil, even if it is of poor quality, there will be the presence of forests of coniferous trees (either natural or replanted).

When these coniferous trees are located in areas which are more accessible to humans, usually give rise to logging industries.

Water Supply

Ribbon lakes can form natural reservoirs especially when they are located in very rainy areas.

Glacial troughs may also be ideal located to build artificial reservoirs.

These reservoirs, both natural and man-made, have the potential of supplying the locals with ample fresh water supply for daily use.

Energy Sources

Wind Energy:

Exposed hillsides also provide ideal sites for wind farms to be developed.

HEP – Hydro-Electric Power:

Hanging valleys provide a natural ‘head’ of water needed for to turn turbines in hydro-electric power stations.

Tourism

Areas with glaciers or winter snow are often a perfect locations for ski-resorts.

Mountains are also ideal for rock climbing, hiking and scenic views.

Ribbon lakes can also be used for water sports.