Glacial Landscapes Flashcards
What is plucking?
As the ice moves over the rock surface below, meltwater freezes around loose sections, pulling them away. Plucking is especially effective when the rock contains many joints (cracks) which the water can seep into.
Why is meltwater present under a glacier?
The sheer weight of ice above. Ice at the base of the glacier melts because of the great pressure it is under( this is called pressure melting). Also, meltwater has travelled from the surface of the glacier to its base through crevasses in the ice
What is abrasion?
Erosion is caused by rocks and boulders embedded in the base of the glacier. These act like sandpaper, scratching and scraping the rocks below. Very large boulders can do enormous damage this way, scarring the landscape with features called striations. These are still visible in the UK today.
How are striations formed?
Very large boulders scrape along the rocks below and scar the landscape.
What increases the rate of abrasion?
When a lot of plucking has taken place, large numbers of rocks and boulders become embedded into the ice.
Where does freeze thaw weathering take place in glaciated areas?
Takes place on rock surfaces above the surface of the ice and at its margins
How does freeze thaw weathering take place?
Water seeps into cracks in the rock face
The temperature falls at night, causing the water to freeze
Water expands by 9-10% when it turns to ice. This expansion puts pressure on the rock either side of the crack, prising it apart and causing the crack to tear wider open.
During the next 24 hour cycle, the ice melts, sinks deeper into the crack and then freezes again
Over time large boulders of rock can be shattered apart by repeated cycles of this weathering process
How is freeze thaw weathering evident?
Seen in landscape features called scree slopes and block fields.
What is the difference between weathering and erosion?
Erosion requires a moving force like ice to break apart rock and carry it away. In contrast, weathering describes the destruction of rock that take place in a particular place. Weathering is caused by temperature and moisture changes along with any chemical processes.
How do glaciers move?
Glacier ice forms from snow that is compressed
As the weight of the ice accumulates, gravity causes it to flow over the lip and down the mountain
The surface of the glacier cracks as the glacier moves over the uneven valley floor. Deep crevasses form.
The glacier slide over the underlying rock on a film of meltwater (basal flow). The ice speeds up and slows down in response to changes in gradient (internal deformation)
As the glacier moves, the valley floor and sides are eroded by plucking and abrasion. In result lots of moraine is left carpeting the valley floor
As the glacier descents the climate gets warmer, rock debris is deposited to from moraine
The end point of the glacier is called the snout. Large amounts of meltwater pour off the snout of the glacier qnd can carry debris far beyond here.
How does a glacier transport material?
The snout bulldozes material, soil, rocks and boulders are shoved forwards by the force of the glacier
Material is also carried in the surface of the glacier (conveyor belt model)
Plucking tears away rock and this becomes embedded into the glacier
Some rocks fall into crevasses which result in material being carried along the ground and deep inside the glacier
Why does deposition take place?
Deposition takes place when the glacier moves into lowland areas. The rocks that have been carried are deposited as the snout melts as the temperature gets warmer.
What is the dumped material of a glacier called?
Till
What is the sediment called that meltwater rivers carry?
Glacial outwash
How are upland areas affected by ice erosion?
Glaciated places across the world are home to unique landforms that give them a special character that is not found elsewhere.
