Trinity CE High School Geography Department revision: Glaciation

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 Water enters cracks in rocks It freezes and expands forcing the crack slightly wider It melts then refreezes, forcing the crack open even more Eventually after several cycles the rock breaks apart 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.