UNIT 5WEATHERING: (B) GLACIERS Glacier-large long-lasting mass of snow compacted & recrystallized, first into firn then glacial ice. Glaciers part of hydrosphere. Cryosphere includes glaciers sea ice.
75% worlds fresh water is locked up in glacial ice. A. Formation of Glaciers. Glaciers only form where more snow accumulates during the winter then melts away during spring & summer, this is zone of accumulation. Glaciers due to high altitude, cold climate
1. Alpine glacier-mountainous regions can flow forming valley glaciers.
2. Continental glaciers-covers large land masses in polar regions in form of ice sheets. Greenland & Antarctica Glaciers reflect sunlight. Glacial ice affects global heat transport Affects sea level.
Annual layer snow, melts, refreezes, forms ice. Weight ice compresses lower layers into hard crystalline ice. Mass becomes thick, lower layers flow plastically.
3. Anatomy of a Glacier a. Advancing glacier gains more snow than it loses: positive budget. Terminus of glacier advances downslope. b. Receding glacier has negative budget. Terminus of glacier shrinks back upslope. c. Zone of accumulation snow is added. d. Zone of ablation melting occurs or calving of icebergs.
e. Equilibrium line separates accumulation & ablation zone, will advance or retreat depending on climate.
LEARNING OBJECTIVES: IDENTIFY THE LANDSCAPE FREATURES THAT GLACIERS FORM. EXPLANIN HOW GLACIERS MOVE AND DESCRIBE THE DIFFERENT TYPES OF GLACIER DRIFT.
4. Movement of glaciers Valley glaciers & ice sheets move downslope by gravity. Movement occurs by basal sliding & plastic flow of lower part of glacier. Crevasses fractures formed in upper rigid zone during glacier flow.
Due to friction, glaciers flow faster at top center slowest along its margins.
5. Glacial Erosion Glaciers erode underlying rock by plucking of rock fragments & abrasion as they are fragged along
Basal abrasion polishes & striates underlying rock surfaces/produces fine rock powder called rock flour surfaces
6. Erosional Landscapes Produced by valley glaciers: U-shaped valleys Hanging valleys-smaller tributary glacial valleys stranded above more quickly eroded central valleys.
Cirques-steep-sided, half-bowl-shaped recesses carved into mountains at the heads of glacial valleys,
Arêtes-ridges separating glacial valleys.
Horns-sharp peaks remaining after cirques have cut back into mountain on 3+ sides.
7. Glacial Deposition Till-unsorted unlayered glacial sediments. Lateral moraines-elongated low mounds of till along the sides of valley glaciers.
Medial moraines- moraines trapped between adjacent ice streams.
End moraines-ridges of till piled up along the front end of a glacier. Recessional moraines-successive end moraines left behind by retreating glaciers.
Liquid water flows over, beneath and away from ice at end of glacier. Sediments deposited by this water is glacial outwash.
Sediment-laden streams emerging form braided channel patterns.
Kame- steep-sided mound of stratified sand & gravel deposited at or near the terminus of glacier.
LEARNING OBJECTIVE: Explain the causes of the most recent ice age.
Esker- narrow, often sinuous embankment of course gravel & boulders deposited in the bed of meltwater stream in tunnel within stagnant ice in ice sheet.
Drumlin-smoothly rounded, oval hils of glacial till, formed by the moving ice.
Kettle lakes- water from ice melt left behind. Varves-annual sediments deposited in glacial lakes which can be counted like tree rings.
Glacial trough- deep, steep-sided rock trench formed by alpine glacier erosion. Fiord-narrow, deep ocean inlet partially filling a glacial trough
Erratics- large transported boulders.