Glaciation

Question 1

Formation of a Corrie, Arete and Pyramidal Peak.

Answer 1

1. Snow on north facing hollow recieves less sun so doesn’t melt and piles on top of eachother.
2. More snow piles on top compcting bottom and pushing the air out which creates glacial ice (nevee or firn).
3. As mass increases weight and gravity causes rotary action out of the hollow (rotational slip). Gravity pulls it down hill.
4. Loose rock at the bottom of the hollow is pulled out through plucking which is whend due to friction glacial ice melts as it passes over rocks. It refreezes due to pressure and continues moving, ripoing out the rock.
5. A gap at the back of the hollow called the bergschrund is formed when the ice pulls away. This gap allows melt water to get under the ice and freeze-thaw can take place, thus providing more loose rocks that can be plucked.
6. Freeze-thaw weathering is when water collects in cracks in the rock and freezes, expanding by 9%. This puts pressure on the surrounding rock. The process repeats splitting the rock into large fragments. These are embedded into the ice or will collect at the bottom of a cliff due to gravity. This is called scree.
7. The debris stuck to the bottom of the glacier acts the sandpaper when the glacier moves thus deepening and steepening the hollow. This process is known as abrasion.
8. At the front of the hollow, as the ice rotates out, it exerts less pressure and so a lip is formed. During warmer periods, a little ice may melt, depositing debris on the lip also. This can trap rainwater and is known as a corrie lochan or tarn.
9. A named example is Red Tarn in the Lake District.
   Arete
10. An arete is a knife edged ridge thatseparates two corries.
11. It is formed through frost shattering which is when ice melts into cracks in the rock and ends up refreezing and expanding by 9%. This puts pressure on the surrounding rocks and creates more cracks. They then shatter into large fragments.
12. Peices of rock known as screecollect at the bottom of the slope due to gravity.
    Pyramidal Peak
13. When a three or more corries form back to back around a mountain they created a sharp pyramid shape separated by knife edged ridges called aretes. This is called a pyramidal peak.
14. A named example is Helvellyn in the Lake District.

Question 2

Formation of a U-Shaped Valley and Hanging Valley

Answer 2

1. The weight of the glacier and gravity causes them to flow downhill following an existing v-shaped valley.
2. As the glacier moves, it plucks material from the side of the valley. Plucking is when due to friction, glacial ice melts as it passes over rocks. It refreezes due to pressure. As the glacier advances it rips out the rock.
3. Material stuck to the bottom of the glacier also scours and scrapes at the bottom and sides and acts like sandpaper, wearing away the land. This is known as abrasion.
4. These processes deepen, steepen and straighten the valley.
5. Former interlocking spurs may be cut off as the glacier flows downhill leaving truncated spurs and steep valley sides. This changes it from a v-shaped to a u-shaped valley.
6. The width and shape of the resulting glacial trough will depend on the nature of rock type and intensity and weight of the glacier. A softer rock will erode more easily than a more resisitant rock.
7. Tributary valleys have smaller less powerful glaciers which result in less deep u-shaped valleys hanging above the main valley. These are known as hanging valleys.

Question 3

Formation of a Ribbon Lake

Answer 3

1. A ribbon lake is a long narrow lake that sits in the bottom of a u-shaped valley.
2. When the glacier moves down through the v-shaped valley under its own weight and due to gravity, it will erode a u-shaped valley for itself.
3. It will sometimes reach an area where the rock and soil below is much softer. This means that the glacier is able to gouge much deeper into the valley floor creating a long narrow deep area in the base of the valley. This is done through the process of abrasion. Rocks that are embedded into the bottom of the glacier scrapes across the valley floor like sandpaper wearing away and removing the rock.
4. After the ice age, the water from the misfit stream will fill up the basin creating a ribbon lake.
5. It can also be formed by the glacier increasing in weight and erosive power causing it to surge forward. This could be during colder periods where more snow and ice is being added in the corrie, thus adding weight.

Question 4

Formation of terminal moraine

Answer 4

1. Terminal moraine is a ridge across the valley made up of glacial deposits, till, boulder clay which is unsorted so has just been dumped by the ice.
2. As the glacier moves downhill it acts like a bulldozer, pushing sediment in front of its snout as it goes.
3. On reaching lower altitudes and when temperature rise, the glacier melts, losing power and depositing the moraine that it has been pushing along.
4. Terminal moraine marks the furthest point a glacier reaches.
5. Once the ice has retreated, the terminal moraine can often form a natural dam creating a moraine dammed lake.
6. The glacier can move like a conveyor belt and if it stays in the same place material can be moved to the front adding to the terminal moraine.

Question 5

Formation of a drumlin

Answer 5

1. Drumlins are elongated hills made up of unsorted glacial deposits/moraine/till/boulder clay.
2. Drumlins are formed as the glacier becomes overloaded with sediment and deposits it, streamlining the sediment as it flows over it.
3. It can also be created during warmer periods where the ice melts a little, depositing ground moraine carried beneath it but is still moving forward downhill, under gravity, and thus shaping the moraine.
4. Furthermore, if there is a small obstacle on the ground such as a particularly resistant rock, this may act as a trigger point and till/boulder clay can build up around it.
5. The steeper blunt ‘stoss’ slope faces up valley in the direction the glacier came from and the more gently sloping ‘lee’ slope faces down valley.
6. Drumlins may be reshaped by further ice movements after being originally deposited.
7. Drumlins are found in swarms or in a ‘basket of eggs’ topography.

Question 6

Formation of an esker

Answer 6

1. Eskers are meandering ridges formed by meltwater streams in or underneath a glacier.
2. They are therefore made up of meltwater (fluvioglacial) deposits such as sands and gravels. These are sorted by size with larger stones at the base because larger stones are dropped first by flowing water.
3. The stones also tend to be more rounded than unsorted glacial deposits, because of the action of flowing water and other stones rounding the edges by erosion. This process is known as attrition, where rocks carried along in the water hit off of each other them, chipping away and rounding them.
4. As the glacier melts, sub-glacial streams flow through tunnels and the load is deposited on the floor of the u-shaped valley.