Chapter 17 Flashcards
Glaciers
Ice sheets
Permanent layer of ice covering an extensive tract of land, especially polar regions. (EX: Laurentide in Canada 10,000 years ago)
Ice shelf
Floating sheet of ice permanently attached to a landmass, an extension of an ice sheet.
Ice caps
Smaller ice sheets (less than 50,000 square km)
Ice streams
Fast moving regions of an ice sheet. (EX: Antarctica, 50 km wide 800 m/year)
Alpine glaciers
Formed in valleys originally occupied by streams, have velocities up to several m/year, and are 10 –100 km in length. Creates hanging and U-shaped (trough) valleys that when flooded becomes fiords;
cirques that become tarns when ice is gone; aretes and Horns (peaks)
Outlet glaciers
Allow ice to move downhill away from an ice sheet or ice cap.
Piedmont glaciers
Occur at the base of a mountain.
Formation of glacial ice
Similar to metamorphism in that the ice changes from one solid form (snowflakes) to another (ice crystals).
Internal deformation of glaciers
Occurs within glaciers where pressure is high enough to allow plastic deformation. Above this depth, ice is brittle and crevasses form.
Basal slip
When ice is frozen to a bed, or lubricated by water
Soft bed deformation from ice
Occurs where bedrock is weak enough to deform with ice.
Antarctic glacial movement rate
1-2m/yr
Outlet glacier movement rate
800m/yr
Accumulation zone
Snowfall exceeds summer melt.
Ablation zone
Summer melt exceeds snowfall.
Mass balance (budget) of glaciers
Depends on relative amounts of accumulation and ablation. When accumulation is greater the glacier advances, when ablation is greater the glacier retreats. Separated by an equilibrium line with elevation ranging from 0-5km.
Glacial erosion (2)
- Plucking produces blocks similar to frost wedging
- Abrasion grinds down bedrock to produce rock flour and gives glacial streams a milky appearance/lakes a blue color.
Glacial deposition/drift
Glacial deposits are found in virtually the whole of Canada
Less (minimal) chemical weathering than in river sediments, so minerals such as hornblende and feldspars are common
Till
Material directly deposited by glaciers. Poorly sorted. Becomes tillite when lithified.
Stratified Drift
Material deposited by meltwater into outwash plains and valley trains. Sorted by size/weight of particles.
Kettles
As a glacier retreats blocks of ice can become buried. When they melt, a pit is formed.
Ice-contact deposits
Formed during retreat by fluvial processes and include eskers and kames
End moraine
Terminus of alpine glacier or ice sheet when there is a period of equilibrium
Ground moraine
Deposited as glacier advances. Smooths surface and fills in holes
