1. Glaciers and the Great Ice Ages

2. Pleistocene Epoch: the Great Ice Ages
2.0 Ma to 10,000 years ago
Four (or more) distinct episodes expansion and melting of ice sheets (continental glaciers)
Each ice advance lasted for 40,000 to 200,000 years
Warm spells lasted 10,000 to 30,000 years
Are we living in a warm period now between ice ages?

3. Why did the climate change so drastically and repeadedly?
Climate change and variations in Earth’s orbit
Eccentricity: elliptical to nearly circular cycles
Obliquity: cyclic changes in tilt of axis
Precession: cyclic change in”wobble” of the axis
Variations affect amount and distribution of solar energy received by Earth
Milankovitch cycles are in the right time range to possibly explain cyclic changes in climate

4. How does a glacier form? Cold climate is necessary
Annual snow accumulation is greater than annual rate of melting
Snow builds up over time
Snow recrystallizes to ice

5. Glacial Flow
Ice begins to flow (plastic deformation) under the influence of gravity
Glacier = mass of flowing ice

6. Glaciers are dynamic
Flow is constant
Some parts of glacier are melting
Rate of accumulation vs. rate of melting determines if glacier will advance or if end of glacier will melt back (glaciers never flow backwards)

7. Glaciers and Landscapes
Flowing ice picks up sediment, soil, etc.
Breaks loose pieces of bedrock
Modifies landscape by erosion and deposition

8. Erosion by Glaciers
Striations: “scratch”marks made as ice drags rocks across bedrock

9. Erosion by Glaciers
Modifies “V” shaped river valleys to a “U” shape

10. Deposition by Glaciers
Erratics – pieces of “exotic” rock left by glacier
Till – unsorted, unstratified sediments dumped by ice
Outwash – sorted and stratified sand and gravel deposited by meltwater

11. Deposition by glaciers
Lacustrine sediments
Lakes form between melting edge of ice and obstructions (often deposits of till)
Fine silt and clay settle to the bottom in calm water
Clay may be used in pottery and brick making
If lakes drain or fill with sediment:
bogs and swamps – ecologically important wetlands
Water-logged lacustrine sediments may cause tilting and sinking of buildings constructed on them

12. Glaciers and Landforms
Characteristic landforms