glaciers. a thick ice mass that originates on land from the accumulation, compaction, and...
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Glaciers
• a thick ice mass that originates on land from the accumulation, compaction, and recrystallization of snow.
• Agents of erosion – acquire, transport and deposit sediment
• Occupy ~10% of land area• “Interrupts” hydrologic cycle by “locking
up” water
Glacier
Glacier TypesGlacier Types
1. Valley (Alpine)
• Found in mountainous areas
• Smaller than ice sheets
• Lengths greater than widths
• Only cover a small region
• Transform V-shaped valleys into U -shaped valleys
Alpine Glaciers
Glacier Types
2. Ice sheets (Continental glacier)
• Large scale – cover 10% of Earth’s land
• Found in polar regions
– Greenland – 1.7 million km2
– Antarctica – 13.9 million km2
Continental Glaciers
Fig. 16.3
Daily Questions
The images were taken at the same location but with 59 years between the photos. 1)Which direction is the ice moving (upslope or downslope)?2)Which direction is the glacier moving (upslope or downslope)?3)Is there a difference between the directions – explain.
Upslope
Glacier movement
•Gravity primary force
•Entire ice sheet moves 5 to 50 m/yr
– Plastic flow – flowing solid
– Basal slip – movement over bedrock
•Fastest movement within the center
•Friction Slows down the sides
Glacier movement
20 meters
100 meters
Glacier movement
Glacier BudgetGlacier BudgetIn - Zone of accumulation
Snow accumulates and forms ice
Outer limit is the snowline
Out – Zone of wastage
ablation – general term for loss of ice or snow from a glacier
1. Sublimation
2. Melting
3. Evaporation
4. Calving - icebergs
• If ice formation is greater than ice loss – glacier advances downslope
• If ice formation is less than ice loss – glacier retreats upslope
• If ice formation is = ice loss – glacier position is stationary
Zone of Accumulation Zone of Wastage
Glacier budget
Glacier Erosion and Deposition
Plucking – loosen and lift blocks of rock (mechanical weathering)
Abrasion – sediment in ice acts as giant “sandpaper”
Creates Rock flour – very fine-grained material
Creates Striations – grooves scratched in bedrock that indicate direction of ice movement
Causes of Glaciation
• Full Reasoning is not known
• Theory of Glaciation needs to include:– Interglacial periods – periods of warm climate
separating periods of glacial advancements.
Causes of Glaciation
• Full Reasoning is not known
• Theory of Glaciation needs to include:– Interglacial periods – periods of warm climate
separating periods of glacial advancements.– Glacial episodes in the Paleozoic (200-300
mya) and Precambrian time (700 mya).
Causes of Glaciation
• Full Reasoning is not known• Theory of Glaciation needs to include:
– Interglacial periods – periods of warm climate separating periods of glacial advancements.
– Glacial episodes in the Paleozoic (200-300 mya) and Precambrian time (700 mya).
– Earth’s average global is 14oC, in the geologic past it was 22oC – Glaciation requires a temp. of about 10oC.
– Continental glaciers originate in polar or elevated land.– Sufficient precipitation needs to occur.
Milankovitch cycles
• Earth’s orbital changes controls its climate
• EccentricityEccentricity– Measure of the nooncircularity of Earth's orbit– Cycle is about 100,000 years
Milankovitch cycles
• EccentricityEccentricity
• InclinationInclination– The changes in the axial tilt (22o to 24.5o) of the
Earth– The greater the tilt the greater the contrast
between summer and winter temperatures– Cycle is about 41,000 years
Milankovitch cycles
• EccentricityEccentricity
• InclinationInclination
• PrecessionPrecession– The wobble of the Earth as it spins on its axis– Cycle is about 26,000 years
Milankovitch cycles
• Main effect of cycles is to change the contrast in the temperature of the summer and winter.
• Glaciation would occur when the summer temperature is closer to the winter temperature, but winter temperature are not colder than usual.
• Rather the mild summers melt less ice than is received in the winter.