Glaciology I Flashcards
Why is Glaciology important?
Understand past and present cryosphere behaviour to predict future.
Globally population is concentrated close to sea level.
Hazards- flooding and drought
Resources- water
Major landform and sediment producer
Glaciology in the news
Pine and Thwaites Glacier
Two glaciers that are moving quickly in Antarctica.
They are also retreating very quickly.
If they suddenly retreat, more ice would come in behind then (water too) and create an even bigger retreat in Antarctica.
It would dramatically effect sea level.
Glaciers and climate change
There is a lot of overlap but…
Climatic effects on glaciers include radiation and precipitation.
Glacial effects on climate include albedo and changes to jet stream.
Glacier motion
Three elements make up the surface velocity of a glacier:
Creep (Uc)
Sliding (Us)
Till deformation (Ud)
U = Uc + Us + Ud
What is Creep?
Ice is a semi viscous material and moves under its own weight
Glen’s Law
e = Aτn Where: e = strain rate A = temperature τ = shear stress n = 3
Shear Stress
Τ = pgh sinα Where: p = density of ice g = gravity h = thickness of ice α = slope angle
Implications of Glen’s Law
e = Aτn
If τ is doubled (e.g. double the thickness)- deformation rate (movement) increase 8 times.
Warmer glaciers flow faster
Shallow approximation model
Uc = 2A/ n + 1(pgsinα)nHn + 1
Where h = glacier depth
Basal sliding
This occurs when…
There is a thin layer of melt water at the base of the glacier (Weertman, 1964)
Boulton and Jones (1979) showed that…
90% of glacier motion could take place in the underlying sediment, if a glacier rested on an unconsolidated bed.
Σ = (Pi - Pw)tanφ + C
Pi = pressure of ice Pw = pore water pressure (Pi - Pw) = effective pressure tanφ = property of the sediment C = a constant
Effective pressure
Pi - Pw
High effective pressure = rigid bed
Low effective pressure = deforming bed
What are sticky spots?
Slower/ stationary parts of deforming bed (Alley, 1993)
Bedrock
Stiffer till
Frozen patches
Stick slip motion
Stick (ice and till moving together, slowly)
Slip (just the ice moving, rapidly)