Glacial History of the Great Lakes

To Do:
- Angus Cruise Reflection Essay (if participated already)
- Week 6 Discussion – Geoengineering Glaciers (due Friday, Oct. 3)

After this week, students should be able to:

Explain the role of glaciers in the hydrologic and rock cycles.
Describe the different types of glaciers, their characteristics, and their present-day distribution.
Describe how glaciers move, including the rates at which they move and the significance of the glacial budget.
Discuss the processes of glacial evolution and identify major topographic features sculpted by glacial erosion.
Distinguish between the two basic types of glacial deposits and briefly describe features associated with each.
Summarize current ideas about the causes of ice ages.
Discuss the extent of glaciation and climate variability during the Quaternary Ice Age.
Identify evidence of glaciers around the Great Lakes Region.

Understanding the implications of glaciers and their relevance within the Great Lakes course.
Importance of glaciers to Earth's climate and geography.

Existence controlled by Earth's changing climate.
Current glacier coverage: approximately 10% of Earth's surface.
Represents the equivalent of an ice sheet nearly 1 mile thick over the entire North American continent.

Process of recrystallization:
- Accumulation of snow leads to compaction, which loses trapped air, increasing density.
- Melt and refreeze transform snowflakes into small, rounded crystals known as firn (density 0.4 - 0.8 g/cm³).
- Continued compression leads to formation of larger ice crystals termed glacial ice (density of 0.9 g/cm³).

Glaciers serve as indicators of climatic history:
- Each layer of ice captures atmospheric gases from the year of formation.
- Records of climate can extend back approximately 800,000 years.

Originating at high altitudes, these glaciers move downslope due to gravity.
Characteristics:
- Usually longer than they are wide.
- Flow like rivers confined within rock walls.

5th largest continent, over twice the size of Australia.
Recognized as the coldest, driest, windiest, and highest continent on average.
Contains West and East Antarctic Ice Sheets separated by the Transantarctic Mountains.

McMurdo Station: Largest U.S. scientific research station, supporting over 1,200 residents during summer, decreasing to about 1,000 in winter.
No permanent human residents live in Antarctica.

The glacier's margin can advance, retreat, or remain stationary based on its glacial budget.
The glacial budget is the balance between
- Accumulation (gaining mass) at the glacier's upper end.
- Loss (wastage) at the glacier's lower end.
Indicators of glacier health:
- If accumulation exceeds wastage, the glacier advances.
- If warming increases wastage or lowers snowfall, the glacier retreats.

Glaciers move similarly to rivers; their flow rates are highest in the center, which contrasts with the slower movement near the edges due to friction from valley sides or substrate.
Crevasse: A fissure in the glacier's surface observed within the zone of fracture.

Glaciers can erode vast volumes of rock and sediment through two primary methods:
- Plucking: When glaciers flow over fractured rock, they uplift and incorporate blocks of rock into their mass.
- Abrasion: The ice, filled with debris, acts akin to sandpaper, smoothing and polishing underlying surfaces.
The resultant pulverized rock is termed rock flour and is often responsible for glacial striations, lines observed on bedrock.