Flashcards
PW4
Cards in this deck (18)
- 1How does ice move from accumulation to ablation?
- 2How can photos show glacier movement?-Show it over a known time scale where it has been and where it is now
-Can quantify the speed of the ice movement
-Links to hydrology under it - 3How can a glacier move?-Ice flow
-Glacier sliding
-Sediment movement
-Ice deformation
-Sediment deformation - 4How can ice deform?-The warmer the ice is (but still less than 0) the softer it is and therefore the more likely it is to flow and fold
- 5What is the equation for ice deformation?
- 6What may this be influenced by?-Temperature
-Water quality
-Amount of debris in ice - 7How does surface motion alter with ice deformation with depth?Friction at valley sides and therefore it slows down glacier movement
-Fastest speed of ice movement will be at the top of the glacier in the centre
-Highest rate of ice deformation in the glacier will be at the bottom
-Ice is thickest here. - 8Why does ice fracture occur?-When ice cannot creep fast enough to adjust its shape for a given stress
-Strain rate of ice depends upon ice surface slope and thickness
-Shear stresses altered by longitudinal stresses from up and down the glacier
-Extending flow increasing the tensile stress
-Sheer stress exceeds the strain rate of the ice leading to brittle failure or fracture - 9How to crevasses form?-Ice in front is moving faster than the ice behind and therefore ice cannot deform fast enough to change its shape and therefore it begins to break apart
- 10Why do crevasses never each the glacier bed?-The cold surface layer of a glacier is very brittle
-At depth, creep rates are high enabling the ice to deform faster than it cracks apart
-Crevasses therefore never penetrate to the bed
- 11How can glacier beds affect the rate of movement?-Sliding
-On a smooth bed, a block of ice would move according to the basal shear stress
-Tb = p g h sina
-In reality glacier beds are not smooth but demonstrate roughness resisting forces
-Ice has to flow past such obstacles - 12How does ice flow move around bumps?
- 13How can deformation of basal sediments affect glaciers?-Many glaciers overlie soft sediments
-Deformation of these sediments can contribute to ice flow
- 14How can water lift parts of the glacier?-Distributed system of linked cavities conveys water under very high pressure
lifts parts of the glacier from the bed and help them to slide forward
locally enhances motion over parts of the glacier bed - 15Does a conduit drainage system enhance glacier movement?-No, conduits usually convey water at a low pressure
-Only cover a very small amount of the glacier bed
-Discrete systems - 16How can subglacial hydrology affect ice movement?-The key issues here is water pressure
-The distributed system of linked cavities conveys water under high pressure
-This lift parts of the glacier from the bed and help them to slide forward
-During summer when there is lots of meltwater the drainage system is formed of a discrete network of large conduits, water is conveyed at low pressure, close to atmospheric
-The glacier is firmly on its bed so no enhanced forward motion by cavity sliding - 17Represent subglacial hydrology in ice movement
- 18—
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- Flashcards on PW4, created by erossmae on 25/08/2015.
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- erossmae
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