Glaciation Revision Session

National 4/5 Geography

What you need to know…1. Formation of Glacial Landforms:– Corrie– Arêtes & Pyramidal Peaks– U-Shaped Valley– Hanging Valley

2. Identification of Landforms– O.S. Maps– Photographs

3. Land Use– Explain Land Use Suitability– Land Use Conflicts– Solutions to Conflict

What evidence is there that this is a glaciated landscape?

Corries

Arêtes & Pyramidal Peaks

U-Shaped Valleys

Glacier FormationGlaciers form when snow is compressed by the weight of more snow falling on top of it.

The snow is first compressed into firn crystals.

It is then further compressed into glacial ice.

Processes of Glacial ErosionFreeze Thaw (Frost Shattering)Water in cracks in the rock freezes and expands.After many cycles of freezing and thawing lumps of rock arebroken off.

PluckingGlacier ice freezes into cracks in rocks and when the glacier moves it pulls out chunks to leave a jagged surface.

AbrasionRocks stuck in the ice grind away the bedrock under theglacier.

Corrie FormationBefore Glaciation:

Snow collects in a natural hollow on the North side of a mountain. The weight of the snow eventually compresses the snow underneath, turning it into ice.

During Glaciation:

The hollow is deepened and steepened by the glacier. Plucking steepens the backwall and abrasion (sandpaper effect) hollows out the bottom. Freeze thaw above the glacier also steepens the backwall.

After Glaciation:

Once the Glacier melts a corrie is left behind. This is an armchair shape with 3 steep sides and 1 open one. A tarn or lochan may be found in the bottom.

Arêtes & Pyramidal PeaksArêtes are formed when 2 corries are found back to back.

Plucking and freeze thaw action erodes the backwall of both corries towards each other.

A steep knife-edged ridge of rock is created.

Where 3 or more corries are located in the same mountainside a pyramidal peak will form.

U-Shaped ValleyWhen a glacier erodes its valley, a classic U shape is formed, with steep side walls and a wide flat valley floor.

U shaped valleys start life as V shaped river valleys that existed before glaciation.

Plucking and freeze-thaw action truncate spurs of rock and steepen the valley sides.

Abrasion deepens and flattens the valley floor. Over time the valley also becomes straighter.

Ribbon LochsAt some points in the U-shaped valley, glaciers erode more deeply than elsewhere because:

1. the rock was softer and more easily eroded

or

2. the ice was thicker at this point and therefore more powerful.

Where ice did this, it would create an overdeepened hollow which after glaciation filled with meltwater to become a Ribbon Loch.

The lake takes on the same shape as the valley in which it was formed – so tends to be long and quite narrow.

Exam Style QuestionWith the aid of a diagram, explain the formation of a corrie. (6 marks)

Tips:• Divide your answer into 3 sections:

– Before Glaciation– During Glaciation– After Glaciation

• Include an explanation of the processes taking place (plucking and abrasion)

Sample Answer: Corrie FormationBefore Glaciation:Corries form in bowl like hollows on the NE sides of mountains (1). A small hollow on the side of a mountain will start to fill with snow all year round as temperatures get persistently colder (1). Over the years this snow will be compressed by the weight of further snow fall to form firn (1) and eventually glacial ice (1).

During Glaciation:The glacier erodes by three different processes. Freeze thaw weathering (1) occurs mainly at the top of the back wall (1). Water enters cracks in the rock, freezes and expands, putting pressure on the sides. Repeated freeze thaw will eventually cause the rock to split and break up, so that it falls down the back of the glacier (1). About mid height of the back wall plucking (1) takes place, this is when water trickles into cracks and again freezes. This time the ice forms a bond between the rock and the glacier itself. As the glacier moves along it literally plucks the rocks attached to it out of the cliff (1). Some of the rock remains stuck to the glacier. At the base of the corrie the erosion is dominated by abrasion (1), where rocks embedded in the glacier are dragged along the rock surface, eroding it make it smooth and bowl shaped (1).

After Glaciation:When the glacier melts it leaves behind a steep backwall and a deep bowl (1), which often fills in with water forming a lochan or a tarn (1).

Sample Answer: Corrie FormationBefore Glaciation:Corries form in bowl like hollows on the NE sides of mountains (1). A small hollow on the side of a mountain will start to fill with snow all year round as temperatures get persistently colder (1). Over the years this snow will be compressed by the weight of further snow fall to form firn (1) and eventually glacial ice (1).

During Glaciation:The glacier erodes by three different processes. Freeze thaw weathering (1) occurs mainly at the top of the back wall (1). Water enters cracks in the rock, freezes and expands, putting pressure on the sides. Repeated freeze thaw will eventually cause the rock to split and break up, so that it falls down the back of the glacier (1). About mid height of the back wall plucking (1) takes place, this is when water trickles into cracks and again freezes. This time the ice forms a bond between the rock and the glacier itself. As the glacier moves along it literally plucks the rocks attached to it out of the cliff (1). Some of the rock remains stuck to the glacier. At the base of the corrie the erosion is dominated by abrasion (1), where rocks embedded in the glacier are dragged along the rock surface, eroding it make it smooth and bowl shaped (1).

After Glaciation:When the glacier melts it leaves behind a steep backwall and a deep bowl (1), which often fills in with water forming a lochan or a tarn (1).

What evidence is there that this is a glaciated landscape?

CorriePyramidal PeakHanging ValleyU-Shaped ValleyArêteRibbon Lake

Land Use in Glaciated Areas

Land Use Suitability in Glaciated Areas

Hill Sheep Farming– Cold & wet climate – poor for growing crops.– Steep slopes unsuited for growing crops.– Thin soils are not fertile enough to grow crops.

Tourism– Amazing scenery for tourist.– Many great routes for hill-walkers.

Positives of Tourism Negatives of Tourism

Creates 3000 jobs related to tourism in the Cairngorms.

Skiing damages vegetation and erodes the soil.

Tourism makes £500 million a year for the Highlands of Scotland.

Footpaths are eroded by feet trampling the soil. Can cost £100 per metre to

mend a path.

Tourism makes up 80% of the local economy.

Salaries for workers are low and employment is seasonal.

Locals can take advantage of tourist facilities.

Tourists make the roads very congested. This increases commute times for

locals.

Land Use Conflicts

Why do you think these two land uses might be in conflict with each other?

What solutions can you suggest to deal with this conflict?

V

Land Use Solutions

Problem: Footpath ErosionSolutions:1. Routes signposted.2. Stones laid on footpaths.3. Footpaths fenced off

from fields.4. New routes planned

away from affected areas.

Problem: Litter & VandalismSolutions:1. Designated picnic

areas with litter bins.2. Park Wardens

supervise and educate.