Transcript Glacial Erosion - Trinity Church of England High School

Glaciation is the impact of glaciers on the landscape
A glacier is a large mass of ice that moves under gravity
A glacier forms when snow falls onto frozen ground one year and does not
melt before more snow falls the next year
If this process continues for many years then it compacts and forms ice
(like you would make a snowball)
As the glacier moves down the valley it shapes the landscape
Glacial Erosion:
• Plucking: this happens when ice at the base of the glacier melts. This
water enters cracks on the valley floor. If it freezes again the rocks
become attached to the glacier. As the glacier moves forward large
pieces of rock are pulled out of the ground and carried with the glacier.
• Abrasion: this is often described as sandpapering. Rocks on the base and
sides of the glacier rub against the rocks as it moves. This wears them
away, often leaving scratches.
Freeze-Thaw Weathering
1. Water enters cracks in rocks
2. It freezes and expands forcing the crack slightly wider
3. It melts then refreezes, forcing the crack open even more
4. Eventually after several cycles the rock breaks apart
5. Also known as frost shattering as the rocks look like they have shattered
These rocks then contribute to the process of abrasion. After the glacier
has melted this material is left behind called a moraine. It can be deposited
in many different ways, creating very distinctive landforms.
Landforms of Glaciated Uplands
Corries: arm chair shaped hollows that have a steep back of bare rock and a
rock lip at the front
They are formed when ice collects in a small hollow on a hillside
When the ice is thick enough it moves downslope under gravity.
As it moves it causes plucking at the base and then the plucked material is
used in abrasion. The ice moves out of the hollow in a rotational manner.
There is higher erosion in the base but at the front there is lower erosion
resulting in the rock lip.
After glaciation has ended the ice will
melt and the hollow will fill with rain
water to create a corrie lake
Aretes and Pyramidal Peaks: If 2 corries form back to back the land
between them becomes very narrow due to erosion. This creates a sharp
ridge called an arete. If corries occur on three or more sides of a mountain
then the top of the mountain will become very sharp and jagged. This is
known as a pyramidal peak
U-Shaped Valley/Truncated Spurs/Hanging Valleys/Ribbon Lakes
As glaciers move through a rivers v-shaped valley they have more erosive
power and erode the valley into more of a U-shape. It also erodes through
the previous interlocking spurs to create truncated spurs. The smaller
tributaries that would have entered the main valley do not erode as much.
Therefore when glaciation ends these smaller tributaries are left much
higher up the valley sides and often appear as a waterfall. Ribbon lakes are
found on the U-shaped valley floor. They can be formed when a ridge of
moraine creates a natural dam and the ice then melts.
Process and Landforms of Deposition
Glacial deposition is the dropping of rock material that was being carried by the
glacier. It mainly happens in the summer when the glacier is melting
This is known as ablation. Deposition also happens due to lodgement. This is when
rocks being carried by the glacier are pressed into the valley floor.
Moraines are the material that was being carried by the glacier that are then left
behind once it has melted.
Material that is left behind at the sides of the valley is called a lateral moraine
If two glaciers meet, their lateral moraines join together to become a medial
moraine
The material that is left behind at the front of the glacier is known as a terminal
moraine
Erratics are rocks that are left behind in an area of different rock type
Drumlins are low elongated hills formed by lodgement of rocks. As the glacier
passes over them it squashes it and streamlines it. They’re often found in swarms
Human Activity in Glaciated Areas
Hydro-Electric Power (HEP)
One example is Dinorwig in north Wales which opened in 1984
It takes advantage of the close proximity of a corrie lake and a ribbon lake
Water from the 80m deep corrie lake (Marchlyn Mawr) is released through
tunnels falling 750m to the ribbon lake (Llyn Peris) driving turbines. From here it
can be pumped back up to Marchlyn Mawr.
Leisure and Recreation
Skiing and hiking are popular leisure activities in glaciated areas
Most ski resorts in the Alps attract visitors for the walking and hiking in
sumer
Hintertux in Austria introduced the White 5 pass that gives people access to
high altitude glaciers
Another new attraction was the Sky Walk near to Salzburg. This is a viewing
platform and on a clear day Slovenia and the Czech Republic can be seen
The Ice palace gives visitors the opportunity to explore inside the Dachstein
glacier.
In 2006/07 low cost flights meant that British people had greater access
Avalanches and Their Management:
Physical Causes:
• Steep slopes – 30-40 degrees have the highest frequency
• Heavy snowfall – which increases the weight of snow on the slope
• Rapid that at the bottom of the snow layer – which can allow the snow to slide
Human Causes:
• Deforestation – because trees help hold snow in place
• Skiing on unstable snow – this may disturb the delicate balance
• Loud noises – explosions or gunfire cause vibrations which disturb the balance
The Montroc Avalanche 1999
• Occurred in February in the Chamonix Valley. As a result of increasing demand
a lot of the trees had been cleared to develop more runs
• There were steep slopes, rising 250m in a short distance
• There had been heavy snowfall in the previous 4 days – up to 2m
• On Tuesday 9th February a wall of 15m high and 300m wide, snow came down
the hillside at speeds of 25m/second. Destroyed 17 chalets, killed 10 people
and badly injured 5
Prediction and Prevention of Avalanches
• Accurate prediction is not possible but the level of hazard can be forecast
• The avalanche warning system in Davos (Switzerland) updates every 15
minutes as 65% of their population live in avalanche hazard areas
• You can also monitor the condition of the snow by digging snow pits and
examining the cross sections to see how stable the layers of snow are
• Building design is vital as roofs should be reinforced to withstand the weight
of the snow on top of
• Barriers can be constructed on slopes e.g. wooden fences, concrete walls.
Afforestation can also be used as trees block/slow down the snow
• Land use planning is vital
• Controlled explosions can be used to trigger small avalanches that cause little
damage rather than allowing large build ups of snow
• Another important aspect is education of people who use these areas
especially those who go ‘off-piste’. Signposts are displayed to emphasise
these messages.