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| Geology 370: Glacial Geology
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erosion: entrainment & subsequent transportation of sediment
rates & patterns
B.
Glacial Abrasion
Abrasion rate affected by:
basal contact pressure (determined by Boulton's or Hallet's model)
basal ice velocity
concentration & supply of rock fragments
removal of glacial flour
Image credit: ©Bruce Molnia, Terra Photographics. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images
Basal contact pressure
Boulton model
abrasion controlled by effective normal pressure (stress) and ice velocity
abrasion and lodgement are part of a continuum
Hallet model
abrasion controlled by rate at which ice flows towards the bed
abrasion highest where basal melting is greatest
lodgement is independent of abrasion
Rock fracturing
fractures may predate glacial advance (e.g. freeze-thaw weathering)
unloading & pressure release
variations in basal ice or water pressure may enhance existing weaknesses
Rock entrainment
rock freezes-on to glacier
Effectiveness depends on:
susceptibility of material to erosion
flow velocity
degree of turbulence
sediment load
Mechanical erosion: abrasion
Chemical erosion
Estimating glacial erosion rates
direct observations
geomorphological reconstruction
sediment volume calculations
Patterns of erosion
primarily controlled by basal thermal regime
other factors
underlying geology
flow velocity
presence of meltwater
previous glacial history
