72905
Glacial erosion processes
- Abrasion
- Material embedded in ice in contact
with valley bottom and sides - rubbing
away as glacier moves. The debris in
the ice acts.
- Fine debris smoothes and polishes rock surfaces
- Coarse debris may leave scratches on rock suface known as striations (or deeper scratches - grooves).
- Glacial debris itself is worn down forming fine material called rock flour.
- Fine debris smoothes and polishes rock surfaces
- Material embedded in ice in contact
with valley bottom and sides - rubbing
away as glacier moves. The debris in
the ice acts.
- Plucking
- Also known as quarrying
- When meltwater enters joints in rocks of
valley floor and sides. Water then freezes
again, glacier freezes onto the rock and as
glacier advances plucks away rock.
- Mainly at base of glacier where PMP may be reached,
resulting in presence of meltwater through pressure melting.
- Most effective in
highly jointed rocks or
where frost shattering
has occurred,
'preparing' the rocks.
- Also known as quarrying
- Rates of glacial abrasion
- Debris shape and size - larger
debris more effective, as is
angular debris (pressure
exerted on smaller area where
rock and debris meet)
- Ice thickness - greater the thickness,
greater pressure exerted on basal
debris and greater rate of abrasion. If
pressure too great, too much friction
and less movement will happen.
- Relative hardness of
particles and bedrock -
resistant debris most
effective especially on
soft bedrock
- Sliding of basal ice
- greater the sliding,
more potential for
abrasion
- Basal water pressure - pressure of
meltwater vital for abrasion to enable
sliding. If water under too much
pressure, glacier may be buoyed up
and debris not under as much
pressure.
- Presence of basal debris - more debris
more abrasion up until point friction takes
over. Basal debris needs to be replenished
as it gradually gets worn away.
- Debris shape and size - larger
debris more effective, as is
angular debris (pressure
exerted on smaller area where
rock and debris meet)
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