Glaciers Flashcards
what is a glacier
slowly moving, thick mass of ice formed by accumulation, compaction + recrystallization of snow on mountains (high altitudes) + near Earth’s poles (high latitudes)
what is a glacier important parts of in the Earth’s system?
Part of the hydrologic cycle (of the hydrosphere)
Important agent of erosion, as part of rock cycle (of the geosphere)
how do glacial ice form
Snow falls on Earth’s surface
If temp remain below freezing, ice crystals in snowflakes recrystallize to form granular snow
Snowflakes become smaller, thicker, and more spherical to produce firn
When thickness of ice + snow > 50m, firn fuses to form a solid mass of interlocking ice crystals – glacial ice
what are the 2 types of glaciers
ice sheets
alpine glaciers
what are ice sheets
immense sheets of ice on a continental scale
Flow radially from areas of greatest ice accumulation
what are alpine (valley) glaciers
Relatively small, occupying mountain valleys
Flow downslope
how do glacial ice move?
Move in 3 ways:
- Internal deformation: ice collapses + flows away from area of thickest snow/ice accumulation under the influence of gravity
- Basal slip: melting point of ice is lower at base of glacier than at surface (due to pressure of overlying ice)
- Liquid water can serve as a lubricant to allow glacial ice to slip over its bed - Materials underlying the glacier (subglacial materials) can deform due to friction w/ the moving ice above
What is the rate of flow within a glacier
Rate of flow within a glacier largely influenced by friction btwn glacial ice + bed of glacier (+ in some cases valley walls)
Flow rate greatest in ice most distant from areas of contact btwn a glacier + the ground
As in rocks, glacial ice tends to undergo brittle deformation (zone of fracture) close to the surface (forming crevasses) but behaves in a more plastic manner at depth
what is the ice budget of a glacier
Snow + ice added in zone of accumulation
Ice lost in a zone of ablation at the leading edge (terminus) of a glacier
The equilibrium line separates zone of accumulation + zone of ablation (where loss of ice is balanced by the gain of ice)
If net accumulation > ablation, the terminus of a glacier advances
If net accumulation < ablation, the terminus of glacier retreats
But ice flow within glacier is ALWAYS moving towards the terminus (due to constant flow toward the zone of ablation
what are glaciers important agents of
erosion
how do glaciers erode underlying bedrock?
Plucking (removing particles from bedrock surfaces)
Abrasion (scratching of bedrock surfaces by flowing ice (aided by rock fragments within the ice)
Bulldozing (mass movement of dislodged particles by moving ice)
what are the erosional landforms produced by alpine glaciers
Glacial erosions modifies V-shaped river valleys into U-shaped valleys
Scoop-like features called cirques, separated by aretes are produced at the heads of glacial valleys
Cirques extend downslope into U-shaped valleys
Small glaciers feed into larger ones that carve deep glacial troughs
After the glacial ice melts, the smaller U-shaped valleys appear to “hang” above the larger glacial troughs (so are called “hanging valleys”)
what are fjords
Deep glacial troughs along coastlines can be flooded by the sea to produce inlets called fjords
what are two main types of sediment deposits associated w/ glaciers?
- till
- outwash
what is a till
Deposited directly by glaciers (typically poorly sorted)
