Glaciation Revision

Sukhvir Lyall, Mitchell Harris, Cameron Whitehead, John

Lutwyche & Alex Weir

SpecificationFreeze thaw and the processes of erosion – abrasion and plucking.  The characteristics and formation of corries, aretes, pyramidal peaks, glacial troughs, ribbon lakes, hanging valleys, truncated spurs, boulder clay/till, moraines and drumlins.

Recognise and describe glacial features on Ordnance Survey maps and photographs. 

SpecificationThe processes should be understood in the context of their role in forming the glacial features listed.  Candidates should appreciate the landscapes produced in areas of glaciation and that it is the assembly of the features that makes the glaciated landscape distinctive.  The use of photographs and Ordnance Survey maps would prove helpful in this context.  Candidates may be expected to name examples and describe the characteristics of the features and explain their formation with reference to the appropriate processes that have been at work.

SpecificationThe human uses of an upland glaciated are to include farming, forestry and tourism.  The social, environmental and political issues currently affecting upland glaciated areas and the management strategies for contemporary issues re conservation and sustainability e.g. grants for conservation, stewardship schemes, repair and maintenance of footpaths, eco-friendly new developments as examples of contemporary solutions.  The conflicts that arise out of the values and attitudes of different interest groups in upland glaciated areas.

SpecificationOne case study e.g. the Lake District, Alps, Rockies, Himalayas is advised to enable students to describe and explain the human uses of the landscape in upland glaciated areas.  Contemporary issues may include depopulation of these remote areas, conflicts between authorities promoting tourism and local inhabitants, environmental degradation etc.  Students should be aware of the different attitudes and values of the groups and examples of the strategies being used to combat the issues. Opportunities prevail for decision makingexercises e.g. on plans for new winter sports facilities or speed limits on lakes etc.

Processes of Glacial Erosion

Plucking Plucking occurs when rocks and stones become frozen to the base or sides of the glacier. The rocks are plucked from the ground or rock face as the glacier moves. The result of plucking is a jagged landscape from the soft and hard rock.

Proceses of Glacial ErosionAbrasion Rocks become stuck in the base and sides of the glacier. They rub against the rock faces as the glacier moves.  The landscape wears away the landscape as the glacier behaves like sandpaper.  It leaves behind smooth  surfaces which may have scratches in them called striations.

Freeze-thaw Weathering

The main process is freeze-thaw weathering. Freeze-thaw describes the action of glacial meltwater on joints, cracks and hollows in rock. When the temperature reaches freezing point, the water inside cracks freezes, expands and causes the cracks to widen.  point.

 

 

When the temperature rises, the water thaws and contracts.  This eventually causes rocks to break up.  For freeze-thaw to take effect, the air temperature needs to fluctuate around freezing point.

 

Forestry and farming

Valley glaciers widen valley floor and make them flat. In upland areas, land on the valley floor is precious for farmers. This is because there is more space and better shelter the valley floor is where the melted glacier deposits most of it's load this gives a greater thickness to the soil 

 

 

Cattle rearing is carried out on the lower part of the valley whereas sheep rearing is predominately on the steeper slopes for rough grazing. Where slopes are too steep for farming coniferous tress are planted this means a new source of income is provided for the farmers.

Glacial Troughs

• Glaciers form very distinctive U – shaped valleys which have steep sides and flat floors.They are formed after V – shaped valleys are formed as they steepen, deepen and smooth the V – shaped valleys. The pictures below show the difference between the U – shaped and V – shaped valleys.

• Glaciers, like rivers, have tributaries. As the main glacier erodes deeper into the alley, the tributary is left, higher up in the steep sides of the valley. If there is a waterfall at the end of a U – shaped valley at the cliff – face, it is called a hanging valley.

• When a river erodes a landscape, there are juts in the river which have formed from ridges of land in the upper course of the river. These are known as interlocking spurs.A glacier cuts through these ridges leaving behind truncated spurs.

Practice Exam QuestionExplain the formation of a glacial trough?Glacial troughs are formed when a glacier widens and deepens a valley from a V-shape into a U-shape. The upper slopes of glacial troughs tend to be very steep, while lower down there is a gentler descent. As the glacier gets smaller the trough will become shallower. Glacial erosion features associated with glacial troughs are truncated spurs which are a result of straightening the valley.

Practise Exam Question

Corries and Tarn Lakes

•  A Corrie is a large circular rock hollow (also called a Cirque)

• They are sometimes, but not always, filled with water, which is called a Tarn Lake

• The Tarn Lake forms after the ice in the corrie has melted and is also usually circular in shape

Formation of a Corrie - Part 1

• Corries begin where neves compact and become ice

• freeze-thaw weathering at the mountain tops create a headwall by plucking loose rtocks

• Water seeps down the bergschrund cutting a steeper backwall

Formation of a Corrie - Part 2

• Plucked rocks abrade the bottom of the hollow

• This causes the bottom of the hollow to deepen, and rotational slip to increase

• The rotational slip movement causes greater pressure at the bottom of the headwall

• This also causes less pressure where the lip of the corrie is formed

Formation of a Tarn Lake

• The corrie provides an ideal place for a lake to form naturally after the ice has melted

• The water accumulated out of meltwater and drain water

• These Tarn Lakes provide idyllic landscapes in areas such as The Lake District

Aretes and Pyramidal Peaks

• An arete is formed when two corries erode back towards each other

• The two back walls come together and form one sharp-edges ridge

• A Pyramidal Peak if formed when three of more corries erode together

• A Pyramidal Peak has a very sharp incline

• A famous example of a Pyramidal Peak is the Matterhorn

 

Example Exam Question - Corries

1. Name features A and B (2 marks)

2. Explain, with use of labeled diagrams if necessary, how a corrie is formed (4 marks)

Answers to Example Exam Question

1. A: An Arete, Pyramidal Peak, Horn or steep back wall

2. Level marked:                    Level one is simple statements such as: "a hollow fills with ice, the ice erodes a hollow" for one or two marks.                   Level two is more complex sentences with reference to glacial processes                            

 

Ribbon Lakes• A ribbon lake is a long, thin

lake formed at the base of many glacial troughs.

• They occur where terminal moraine or a rock barrier stretches across the valley floor, forming a dam

• A famous example of a ribbon lake is Lake Windermere or Wast Water, the deepest English lake

 

Formation of a Ribbon Lake

Hanging Valleys

• A hanging valley is a valley which leads into another valley

• It is distinct as where the smaller valley reaches the main valley, where there is an overhanging ledge at a steep side wall

• The overhanging valley may produce quite dramatic waterfalls

Formation of a Hanging Valley

• Originally, the valleys would have distinct V shapes, with one stream flowing into another

• During glaciation, an alpine glacier grows, and moves through the valley

•  The main trunk glacier erodes a large glacial trough whilst smaller glaciers erode forming smaller glacial troughs, which lead into the main trough

•  The glaciers then retreat leaving the large glacial trough, with many hanging valleys on its side walls

Moraine• All materials transported by glaciers are called moraine.• There are four types of moraine: lateral, medial, ground and

terminal.• Lateral moraine is material that comes from the freeze thaw

weathering of valley sides, which is deposited at the sides of the glacier.

• Medial moraine is found at the centre of the glacier, and comes from two lateral moraines joining together.

 

Moraine• Ground moraine is the

material that is dragged underneath a glacier, which forms the flat valley floor when deposited. It can also be referred to as boulder clay or till.

• The terminal moraine marks the maximum advance of the glacier, and is deposited at the snout, or end of the glacier. This material can build up if the glacier remains in the same place for a long period of time.

Drumlins• Drumlins are smooth, elongated mounds of material, that

are formed parallel to the direction of the ice movement• They often consist of stones and clay (boulder clay), and are

believed to be the result of the load carried by the glacier being dropped when too heavy.

• They occur in swarms, and are said to form a 'basket of eggs' topography

Example Question(c) Drumlins, terminal moraines and lateral moraines are features deposited by ice.Choose one of these and explain its formation.Level marking  Level 1 (1-2 marks) Basic statements, e.g. the ice erodes the land and drops it toform the drumlins, the ice makes the drumlin smooth.Level 2 (3-4 marks)Clear - the ice erodes the valley sides by abrasion, the rocksare frozen into the ice. When the ice melts the rocks aredeposited in mounds when the ices hits an obstacle, the icesmoothes the drumlin as it flows over it.Level 3 (5-6 marks) Detailed on processes of erosion and or mechanism ofdeposition, also on theories on formation of blunt and taperedends reduce velocity recognised.

The Need For ManagementManagement is need in popular areas where more people are likely to be. These places are known as ‘honeypots’. Management is needed to :• Lessen the damage to the environment.• Reduce the conflicts which may arise between local

residents and visitors.Solutions :• Educate people about the country code.• Warn people to keep on the paths and campaigns such as

‘Take your litter home’ .• Lakes and areas are divided up for different activities to

meet more people’s needs.

Glaciation Recap