UK physical Landscapes - Glacial landscapes Flashcards
When was the last glacial period?
Around 18000 years ago
What was the UK like during the last glacial period?
- there were glaciers in the north and west as far as the Severn Estuary - deep valleys and troughs
- land was permanently frozen in the south and east as permafrost
what is an ice age?
a period of long term cooling of the earth’s atmosphere, resulting in expansion of ice sheets and glaciers
what are the 2 periods of time in an ice age?
glacials (cooler periods) and intergalcials (warmer periods)
how much of the earth’s surface is covered by ice today?
10% - from ice sheets in Greenland and Antractica, high places like the Himalayas, and in the Arctic circle
what is the main form of weathering process and what does it do to the landscape?
- freeze-thaw weathering - mostly seasonal (freeze in winter, thaw in summer)
- it creates a jagged landscape, weakens rocks so they are easier eroded, and creates scree which is a powerful erosion tool under moving glaciers
describe freeze-thaw weathering
1) water enters cracks in the rocks
2) when it gets really cold, water freezes and expands by up to 9%
3) when it warms up the ice melts
4) this process repeats many times
5) the pressure of the ice expanding causes the rock to break after many cycles
what are the 2 main types of erosion processes?
- abrasion
- plucking
what is abrasion?
a sandpaper effect caused by rocks frozen into the glacier scouring the valley floor, leaving behind a smooth, polished surface and striations
what is plucking?
meltwater freezes rocks beneath the glacier into it. this rock is plucked away by the glacier as it moves downhill
what are striations?
scratches in the bedrock surface caused by a glacier moving using the process of abrasion
what are the 3 ways glaciers move?
- rotational slip
- basal slip
- internal deformation
what is rotational slip?
the circular movement of ice along a curved surface to enlarge and develop hollows
what is basal slip?
when meltwater lubricates the glacier enabling it to move downhill, mainly in summer months
what is internal deformation?
In winter, the glacier is frozen to the rock surface. The weight of the ice and effect of gravity cause ice crystals to change shape, which causes the glacier to move slowly downhill
how fast do glaciers move?
really slowly - only a few cm per year
how does a glacier transport sediment?
by bulldozing - when rock and debris in front of the glacier are moved downhill by the sheer force of the ice
what is the material transported by glaciers called?
moraine
where does glacial deposition occur?
wherever ice melts, usually at the snout (tip) of the glacier
what is glacial till?
the poorly sorted rock fragments left behind as a glacier retreats
what is glacial outwash?
well sorted sandy, gravelly material moved by glacial meltwater. larger rocks are deposited closer to the ice, fine material is further away
how does a glacier form?
1) Snowflakes fall and accumulate in a hollow on the side of a mountain
2) more snowfall - weight compresses snow -> firn ice
3) more snowfall - firn ice -> ice
4) ice looks blue - sall air is squeezed out under the pressure
5) ice doesn’t melt + more snowfall = glacier becomes bigger and heavier
6) force of gravity makes it move downhill very slowly
7) as the glacier moves it erodes the valley on either side + underneath, changing the landscape
What is a corrie?
a deep depression found on a hillside
also known as a cirque or cwm (Welsh)
how does a corrie form?
1) snow accumulates in a hollow and gets compressed into ice
2) glacier gets bigger - freeze-thaw above, plucking steepens back wall, rotational slip gouges out deep hollow, abrasion deepens the hollow
3) less rate of erosion at the end - ice is thinner - rock lip
4) after glacial period - armchair shaped hollow - the corrie
5) features - jagged summit, steep back wall (freeze-thaw weathering still happens), corrie lake (tarn)
what is an arête?
it is a knife edge ridge with a steep drop on either side
how does an arête form?
when two corries erode back to back and the land gets narrower
what is a pyramidal peak?
a sharply pointed mountain peak caused by glaciation
how does a pyramidal peak form?
when 3 or more corries erode back to back on a mountain leaving behind a peak
what are the main glacial valley landforms?
- glacial trough (U-shaped valley)
- hanging valleys
- truncated spurs
- ribbon lakes
how is a glacial trough formed?
1) before the glacier there was a V-shaped river valley
2) during glaciation, rock in the valley is removed (plucking + abrasion)
3) the glacial trough is formed - a steep sided, wide, flat-bottomed, U-shaped valley