Ice on the Land Flashcards
Name the two types of Erosion?
Abrasion and Plucking
Describe the process of abrasion?
Abrasion occurs when rocks and stones become embedded in the base and sides of the glacier. These are then rubbed against the bedrock and rock faces as the glacier moves. This causes the wearing away of the landscape. It leaves behind a smooth polished surface which may have scratches called striations.
Describe the process of plucking?
When melt water beneath a glacier freezes, it bonds the glacier base to the rocky surface below like glue. As the glacier moves, any loose fragments are plucked away. This process leaves a jagged, rocky surface.
What are the four ways glaciers move?
Rotational slip, Bulldozing, Basal sliding and Plastic flow.
Describe the process of freeze thaw weathering?
Water fills in the crack or joint of a rock. The water freezes and expands exerting pressure on the rock. The crack is widened as a result. Repeated freeze thaw action weakens the rock. Eventually the rock splits and loose parts fall away.
Describe the process of rotational slip?
The base of the glacier, especially in the summer, melts due to friction and temperature. This creates a film of melt water that helps the glacier to move along more easily. This is a basal slip. However when the glacier then moves down hill it is a rotational slip.
Describe the process of bulldozing?
The pushing of deposited sediments at the snout by the glacier as it advances.
Describe the process of deposition?
As the ice melts the moraine it was carrying or pushing gets abandoned and dumped as the ice can no longer carry it as it has melted. Also if the ice slows down and loses energy it deposits its material as it no longer has the energy to hold it.
What are the characteristics of a corrie?
Deep depression in hill side. Steep back wall often with a scree slope due to freeze-thaw action. Often have a tarn (corrie lake) in them. Rock lip holds water in. Lower side walls and arête along the back wall.
How does a corrie form?
Snow accumulates in a slight hollow on a mountain slope. As more and more snow accumulates the weight compresses the snow and turns it into ice. Due to the gravity and the weight of the ice, the ice moves downhill by rotational slip. The back wall of the slope is eroded by plucking and abrasion (with the aid of sediment) which makes the hollow deeper and larger. As the ice melts, a large hollow is left over, often with a lake or tarn in it.
What is an arête?
A knife edged ridge formed between two corries.
How does an arête form?
Two glaciers flow in parallel valleys. The glaciers erode the sides of the valleys which sharpens the ridge between them. Corries are often found around them.
What is a pyramidal peak?
A sharp edged mountain with at least three sides, which peaks have been formed from three or more back to back glaciers.
How does a Pyramidal Peak form?
Three or more corries are formed on sides of the same mountain/hill. The glaciers erode more and more into the hillside backwards. After the ice has melted three or more corries are left with a pyramidal peak left in the middle.
What is a truncated spurs?
An eroded interlocking spur. Often have very sheer cliff faces.
How does a truncated spur form?
Interlocking spurs have been created by a river cutting through the landscape but having to move its way around areas of more resistant rock. However a glacier has much more power than a river and so can erode through harder rock. The interlocking spurs are thus cut off leaving truncated spurs.
What are the characteristics of a glacial trough?
Steep sided, wide valley and flat bottomed.
How does a glacial trough form?
As the glacier moves through a valley its power is able to erode interlocking spurs leaving them truncated. The sides are left very steep and the valley straighter. The valley is left very wide as glaciers are huge. Moraine underneath the glacier abrades the valley floor leaving it very flat.
What is a ribbon lake?
A long narrow lake found at the bottom of a glacial trough. They don’t appear to fit their surroundings as the valley is much wider than they are.
How does a ribbon lake form?
As a glacier moves down a valley it meets bands of rock with differing amounts of resistance. When a band of softer rock is met, the glacier is able to erode it more easily therefore creating a rock basin. When the glacier meets harder rock, erosion occurs less easily, creating a rock bar. After glacial periods have passed and the ice has melted, the depressions left (the rock basins) collects rain water and forms a lake. The rock bars act as a dam holding the water in.
What is a hanging valley?
A tributary glacial trough perched up on the side of the main valley, often marked by a water fall.
