3.1.3.4 Glacial Landscapes in the UK Flashcards
What was the glacial environment like in the UK?
- Snow and ice covering much of the landscape - very much part of the UK during the last ice ago
- Consistently low temperatures, barely getting above freezing
- Development of significant amounts of snow and ice leading to the formation of large glaciers and an ice sheet across the UK
- Huge glaciers radiated from the north and west and carved deep glacial valleys and troughs. Further east the land was permanently frozen with some meltwater rivers
What was a powerful force in the shaping of the physical landscape of the UK?
ice was a powerful force in the shaping of the physical landscape of the UK
In the last glacial period where did ice extend to?
- During the last glacial period ice advanced south in the Northern Hemisphere to cover large parts of Europe and North America
- In the last glacial period, the ice coverage across the UK reached its maximum extent around 18,000 years ago
- In the UK the ice spread as far south as the Severn estuary
- Southern England would have been completely frozen - like parts of northern Canada today
What happens between glacial periods (within an ice age)?
Between the glacial periods there were warmer interglacials which were at least as warm as today’s climate if not warmer
When did the UK experience an ‘Ice Age’ and what has this formed today?
- 2.5mn - 11,300 yrs ago - UK experienced a succession of glaciations - the ‘Ice Age’
- much of UK was periodically covered by ice sheets (glacial period) spreading from Scandinavia
- glaciers carved deep valleys forming today’s mountain landscapes e.g. The Lake District
Which part of the UK remained ice free during the Ice Age?
- only far south of UK remained ice-free
- temperatures here were low and the ground frozen (permafrost) for much of the year
Ice age:
a period of long-term cooling of the Earth’s atmosphere, resulting in the expansion of ice sheets and glaciers
When was the most recent ice age?
most recent ice age, the Pleistocene, began about 2 million yrs ago
What period are we currently in?
We’re currently in an interglacial period that began around 10,000 years ago
What % of the Earth’s land surface is covered by ice and how does this compare to 20,000 years ago?
- Today about 10% of the Earth’s land surface is covered by ice – the only ice sheets are the ones on Greenland and Antarctica
- Ice covered a lot more of the land around 20,000 years ago (during the last glacial period) – over 30% of the Earth’s land surface was covered by ice, including nearly all of the UK
Glacial processes:
- freeze-thaw weathering
- erosion
- movement and transportation
- deposition
What is the main weathering process in cold environments?
freeze-thaw weathering
Freeze-thaw weathering:
- water collects in cracks or holes (pores) in the rock (usually in Summer as there is more liquid water available unlike in Winter due to freezing temperatures)
- as temperature drops at night, this water freezes and expands
- this puts pressure on the rock at the side of the crack - makes crack in the rock bigger
- when the temperature rises and the ice thaws, water will seep deeper into the rock
- this process repeats many times
- eventually pieces of rock break off
Why is freeze-thaw weathering an important process in glacial environments?
- helps to shape jagged mountain landscapes
- rocks become weakened by freeze-thaw weathering making it easier for them to be eroded by glaciers
- piles of large angular rocks, called scree, collect at the foot of mountains - become powerful erosion tools when trapped under moving glaciers (abrasion)
Crevasse:
a deep, open crack found in a glacier
Diagram of freeze-thaw weathering:
Abrasion in glacial environments:
- the ‘sandpaper’ effect caused be the rocks within the ice scouring the valley floor
- abrasion leaves a smooth, polished surface
- scratches (striations) caused by large rocks beneath the ice can often be seen
Plucking in glacial environments:
- when meltwater beneath a glacier freezes and bonds the base of the glacier to the rocky surface below (like glue)
- as the glacier moves, loose fragments of rocks are ‘plucked’ away
- this process leaves behind a jagged rocky surface
Striations:
sharp, straight lines found in the valley where sharp rocks have grinded their way along
Diagram showing glacial erosion:
2 main ways that glaciers move:
- rotational slip
- basal slip
Rotational slip:
- where ice moves along a curved surface to enlarge and develop hollow
- in hollows high up - movement is more curved
Basal slip:
- in the Summer, meltwater acts as a lubricant to the the glacier enabling it to slide downhill
- this type of movement can be quite sudden - occurs more in Summer months
Internal deformation:
- In the winter, the glacier becomes frozen to the rocky surface
- The sheer weight of the ice and the influence of gravity cause individual ice crystals to change shape in a plastic-like way
- This process is known as internal deformation and causes the glacier to move slowly downhill
How do glaciers transport material?
- Rock fragments resulting from freeze-thaw eroded by the ice are transported by the glacier
- This sediment (called moraine) can be transported on the ice, in the ice (buried by snowfall) and below the ice
- As the glacier moves forwards it pushes loose debris ahead of it - transporting it down the hill - bulldozing
How do glaciers form and move?
- Snowflakes fall and accumulate in a hollow in the mountainside
- With more snowflakes, the weight compresses the snow together to form firm - a very firm type of snow
- As more snow falls and more weight is added this firm turns into ice
- The ice appears blue because of all the air that is squeezed out under pressure
- If ice does not melt and snow continues to fall, the glacier becomes bigger and heavier
- Then the force of gravity causes this large ice mass to move downhill very slowly
- As the glacier moves it erodes the valley on either side and underneath it, altering the landscape
Where is deposition of material carried by the glacier usually found and when does this happen the most
- as deposition occurs when ice melts and most melting occurs at the front/snout of the glacier
- deposition of material carried by the glacier is usually found at the snout
- during Summer as temperatures are higher - meltwater pours off the snout of some glaciers
How does glacial deposition occur?
- As a glacier slowly retreats is leaves behind a bed of broken rock fragments called till
- Due to the lack of water to transport it, till is poorly sorted with jagged rock fragments of all sizes - till is also known as boulder clay
OR
- Renewed further movement of the glacier pushes the material found at the snout downhill (bulldozing)
- This build up of sediment can form a hummock (small mound of sediment)
How does deposition occur ahead of the glacier?
- Ahead of the glacier, meltwater rivers will carry sediment away
- This process of attrition will cause rock fragment to become smaller and more rounded
- Sediment is well sorted with larger rocks deposited close to the ice and finer material carried many kilometres away
- This sandy and gravel material is called outwash
What does constant transport of new, debris laden ice into lowland areas result in?
- Constant transport of new, debris laden ice into lowland areas results in the widespread deposition of all of the eroded and weathered material from the uplands
- This deposited material is known as glacial till
Till:
- poorly sorted debris carried by the ice and then deposited when the ice melts
- will comprise of a range of particle sizes and will tend to be angular and having had little water transport
- outwash - carried by meltwater streams - tends to be more rounded and better sorted, with gradually finer material being deposited with distance away from the ice front
Moraine:
deposited material from a glacier