Glaciers

1. Glaciers

2. Glacier • 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

3. Glacier 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

4. Alpine Glaciers

5. 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

6. Continental Glaciers

7. Daily Questions Upslope • The images were taken at the same location but with 59 years between the photos. • Which direction is the ice moving (upslope or downslope)? • Which direction is the glacier moving (upslope or downslope)? • Is there a difference between the directions – explain. Downslope Upslope Downslope Fig. 16.3

8. 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

9. Glacier movement 20 meters 100 meters

10. Glacier movement

11. Glacier Budget In -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 • Sublimation • Melting • Evaporation • Calving - icebergs

12. Glacier budget Zone of Accumulation Zone ofWastage • 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

14. 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

25. 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.

27. 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).

29. 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.

30. Milankovitch cycles • Earth’s orbital changes controls its climate • Eccentricity • Measure of the nooncircularity of Earth's orbit • Cycle is about 100,000 years

32. Milankovitch cycles • Eccentricity • Inclination • 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

34. Milankovitch cycles • Eccentricity • Inclination • Precession • The wobble of the Earth as it spins on its axis • Cycle is about 26,000 years

36. 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.