Lithosphere Flashcards
Freeze thaw
This is when water gets into cracks in the rock and then freezes, because it expands it then breaks the rock away.
Plucking
The ice freezes around chunks of rock at the bottom and sides of the glacier. As the ice then moves it tears the rock away with it.
Abrasion
All the material under the glacier is known as moraine. This mix of rocks and other material act like sandpaper wearing away the valley floor beneath and at the sides of the glacier.
Formation of a Corrie
Snow gathers in a north facing hollow, over time it compresses turning to ice. Due to gravity the ice moves downhill as a glacier. Plucking occurs on the backwall when ice freezes onto the rock, pulling loose rocks away, making it steeper. Abrasion deepens the bottom of the hollow as rock embedded in the ice and acts like sandpaper eroding the hollow. Frost shattering continues to steepen the sides of the hollow, when water in cracks in the rock freezes it expands and weakens the rock causing pieces to break off. Rotational sliding further deepens the hollow floor as gravity causes the ice to move. Friction causes the ice to slow down at the front of the corrie allowing a rock lip to form, which traps melt water leaving a tarn.
Formation of an Arete
An arete is formed when 2 corries meet at the back of one another. Snow collects in the natural north facing hollows. Over time, the snow compacts and turns to ice. Plucking occurs on the back walls when ice freezes on the rock, pulling loose rocks away, making them steeper. Abrasion deepens the bottom of the hollow as rock embedded in the ice acts like sandpaper eroding the hollow. Frost Shattering continues to steepen the sides of the hollow, when water in cracks in the rock freezes it expands and weakens the rock causing pieces to break off. The two back walls meet and a “knife edge” ridge is formed called an arete.
Formation of a Pyramidal Peak
A pyramidal peak is formed when 3 or more corries meet back to back. Snow falls on natural hollows and over time compacts forming ice. The processes of plucking and abrasion take place making the hollows deeper (abrasion) and with steep back walls (plucking), As the corries erode backwards the steep back walls meet at one point creating a peak. Freeze thaw occurs on the peak creating the jagged point. When the ice melts a pyramidal peak is left with at least 3 corries around it.
Formation of a U-shaped valley
Before glaciation there would have been a V-shaped valley that was caused by a river. Over time snow would have gathered and compacted to form a glacier high in the mountains. Due to the force of gravity the glacier would begin to move downhill. The glacier would have acted like a bulldozer eroding everything in its path. The valley would have been deepened and widened through plucking and abrasion. After the glacier melted the valley has changed. The valley walls have been deepened and the valley floor is flat giving it its name, a U-shaped valley. There is often a thin ‘misfit stream’. Given its name because it could not have created the valley itself.
Formation of a Hanging Valley
A hanging valley is formed when a large glacier is joined by a small tributary glacier. The large glacier moves down a V shaped valley and through the processes of plucking and abrasion deepens the valley floor and straightens the valley sides, leaving a large U shaped valley. The same processes of plucking and abrasion take place in the tributary glacier, but at a much slower rate. This is because the large glacier is far heavier and more powerful, and therefore can erode the land more quickly. When the ice melts, a large U-shaped valley is left where the large glacier had been. The smaller glacier leaves a small valley leading into this and “hanging” from the truncated spurs. There if often a waterfall left coming from the hanging valley.
What is Glacial Deposition?
Glacial deposition is material that is transported by the glacial and then deposited when the glacier begins to melt.
Lateral Moraine
Found at the sides of the glacier, Scree, from frost shattering, is an important source.
Scree = tiny rocks from when ice expands during frost shattering.
Medial Moraine
Found down the middle of the glacial surface and occurs when the inner lateral moraines of two glaciers join.
Ground Moraine
Found at the base of the ice. It is also called till or boulder clay.
Terminal Moraine
Found at the front of the snout of the glacier if it is stationary. It represents the maximum advance of the ice.
Formation of Terminal Moraine
Material such as gravel and rock is pushed along by the glacier. The glacier pushes everything in its way, therefore the material is unsorted. The material gathers at the front of the glacier. When the glacier begins to melt the moraine is left at the furthest point that it traveled.
Formation of an Esker
An esker is a steep sided, long unwinding ridge made up of gravel and sand. It is formed when a river of melt-water runs through a glacier. The river deposits sorted material that it can no longer carry. The material is small and rounded by the water. When the glacier melts the river is almost lost from the landscape and the esker is left.
