Glacial Processes and Landforms Flashcards
What percentage of earth’s freshwater is stored in glaciers?
around 70%
what percentage of earths surfaces covered in ice?
around 10%
where on earth is ice stored?
ice sheets (Antarctica, Greenland) valley glaciers
What areas were covered by ice sheets during the last ice age?
large parts of north america and Europe
glaciers have a strong control on…?
average global sea level
what do glacial deposits lead to?
construction aggregate
important aquifers
ice flows under its own weight due to …..
gravity
If downslope force (shear stress, τ) > resisting force (shear strength), then…
ice flows as a plastic
what are some features of glaciers?
zone of accumulation equilibrium line (line between net gain and net loss) zone of ablation crevasses snowlayers
How does snow become glacial ice?
becomes more dense - contains less air
what is the lower limit of the zone of accumulation?
the equilibrium line
what is the zone of ablation defined by?
net loss by melting
if accumulation > ablation
glacier advances
if accumulation < ablation
glacier retreats
ice within a glacier always flows in which direction?
forwards (even when retreating)
how do glaciers move?
creep
basal slip
how fast does the ice in a glacier move?
metres/yr to 100 metres/yr
what are the different types of glaciers?
valley (also tributary/tidewater) glaciers
ice sheets
(they are classified by size/location)
how hard is ice?
1.5 hardness on mosh scale
can be scratched by a fingernail
How do glaciers erode?
Glaciers scour & erode rock
how do glaciers scour & erode rock?
Ice pressure + sediment abrasion
(1) As ice flows, it entrains & ‘pushes’ sediment
- > Abrasion, ‘bulldozing’, & plucking
2) Glacial meltwater
- > Meltwater flow (outwash plains & rivers)
- > Pressurised sub-glacial flow
What landforms result from glacial erosion?
cirques truncated spurs horns tarns arête hanging valleys glacial trough (u-shaped)
what is a roche moutonnée?
Streamlined bedrock mound parallel to ice flow
‘Plucking’ on lee side (freeze/thaw)
What deposits do glaciers leave behind?
(1) Till
(2) Glaciofluvial deposits
(3) Glaciolacustrine deposits
(4) Glacial erratics
what is till?
poorly-sorted mixture of many different sediment sizes and striated rocks [material left behind after transport on/in/under ice]
what are glaciofluvial deposits?
sands/gravels deposited by meltwater channels
what are glaciolacustrine deposits?
fine-grained sediment, with dropstones. Deposited in lakes.
what are glacial erratics?
ice-transported boulders, not derived from underlying bedrock
What landforms result from glacial deposition
eskers (glaciofluvial feature) ground moraines drumlins kettle lakes recessional moraine terminal moraine outwash plain (glaciofluvial deposition)
how are moraines formed?
Debris deposited on ice, up-valley (mass wasted)
Transported on surface, down-valley, down-ice
Leaves train of deposits (till) on margins of glacier, and eventually its front (toe)
what are lateral moraines?
moraines that form along the sides of a glacier
how do medial moraines form?
lateral moraines become medial moraines when two valley glaciers meet
what does a terminal moraine mark?
the furthest advance of the glacier
when are recessional moraines formed?
while terminus of receding glacier remains temporarily stationary
during the last glacial maximum which ice sheet covered all of BC?
cordilleran ice sheet
what is an effect of continental ice sheet on the crust?
During glaciation: crust pushed down
After deglaciation: crust rebounds ->uplift [isostatic rebound]
Forms raised beaches (e.g. Hudsons Bay - still rebounding today)
rate of isostatic rebound is proportional to…..
the viscosity of the underlying mantle (asthenosphere)
what is the global average in temperature fluctuations in the past million years?
around 10 degrees Celsius
what are the milankovitch cycles?
eccentricity tilt precession (variations in earths orbit) they lead to variations in energy received from the sun
what is eccentricity?
where earths orbit fluctuates between circular and elliptical over a 100,000 year cycle
what is tilt?
where earths tilt fluctuates between 22.5 degrees and 24.5 degrees over a 41,000 year cycle
what is precession?
where earth “wobbles” on its axis over a 26,000 year cycle
