Overview
- Lecture explains continental and alpine glaciation, their landforms and effects.
- Emphasis on how massive ice sheets shape landscapes, leave deposits, and impact human interpretation.
- Includes examples from Antarctica, Greenland, North America, and glacial landforms like end moraines, drumlins, eskers.
Continental Glaciation
- Definition: Ice sheets that cover entire continents or large landmasses and flow outward from central accumulation.
- Modern examples: Antarctic ice sheet and Greenland ice sheet (Greenland currently thinning/retreating).
- Snowball Earth: Periods when ice sheets may have covered the entire planet, possibly meeting at the equator.
Effects And Scale Of Ice Sheets
- Ice thickness during last ice age (approx. 21,000 years ago) reached kilometers thick:
- Montreal ~3,300 m (≈2 miles)
- Toronto ~2,100 m
- Boston ~1,250 m
- Chicago ~900 m
- Consequences of thick moving ice:
- Massive bulldozing effect over cities and landscapes.
- Moving ice would destroy structures and level built environments.
- Glacier margins can be abrupt cliffs hundreds of meters high with significant meltwater runoff.
Ice Age Human Migration Considerations
- Crossing ice sheets was not trivial: crevasses, steep ice cliffs, lack of food and animals, extreme cold.
- Walking across the ice sheet (top surface) by whole communities is highly unlikely.
- Safer migration likely occurred around ice margins or exposed land due to lowered sea level, not by traversing ice caps.
Glacial Landforms And Deposits
- End Moraine (endmarine): Ridge of unconsolidated debris bulldozed and deposited at glacial margin.
- Appears as a ridge often with swampy depressions behind it.
- Forms where glacier stopped and dumped plucked material.
- Ground Moraine (groundmarine): Wet, mucky, variably deposited debris left behind glacier interior.
- Often flat, swampy areas behind end moraine.
- Meltwater redistribution:
- Meltwater moves fines further inland; winds pick up fine dust and deposit loess.
- Loess creates highly fertile soils (prairie/Midwestern breadbasket soils).
Eskers
- Definition: Long narrow ridges of well-rounded gravel and sand deposited by subglacial meltwater streams in ice tunnels (ice caves).
- Formation:
- Meltwater flows in confined tunnels beneath glacier, carries and sorts sediment.
- When glacier retreats, the sediment-filled tunnel remains as a sinuous ridge.
- Field clues: parallel ridges of gravel, rounded pebbles indicate water transport.
Drumlins
- Definition: Elongated, parallel hills composed of compacted glacial till, formed under flowing ice.
- Shape: Steep upstream (stoss) side facing the ice, gentle downstream (lee) slope pointing in ice flow direction.
- Interpretation:
- Arrangement and shape indicate direction of glacier movement.
- Formed by the glacier shoveling and compacting unconsolidated material into streamlined hills.
Soil And Agricultural Impact
- Glacial deposits plus wind-blown loess created extremely fertile soils in Midwestern U.S. and southern Canada.
- These soils support high agricultural productivity (wheat, corn).
- Similar fertile regions exist in places like the Ukraine.
Reading Topographic Maps For Glacial Landscapes
- Key map clues:
- Discombobulated contour lines and swampy symbols suggest ground moraine and post-glacial wetlands.
- Long parallel ridges of gravel with regular spacing suggest eskers.
- Parallel, elongated hills with steep and gentle slopes indicate drumlins and show ice flow direction.
- High-elevation contours, cirques, U-shaped valleys, and presence of "glacier" labels indicate alpine glaciation.
Key Terms And Definitions
| Term | Definition |
| Continental Glaciation | Large ice sheets covering continents, flowing outward from central accumulation. |
| Alpine Glaciation | Glaciers confined to mountain valleys; creates cirques, horns, U-shaped valleys. |
| End Moraine (Endmarine) | Ridge of debris deposited at glacier margin where ice stopped or stood. |
| Ground Moraine (Groundmarine) | Unsorted, often wet and mucky sediment left beneath an ice sheet. |
| Esker | Sinuous ridge of sorted sand and gravel deposited by subglacial meltwater streams. |
| Drumlin | Streamlined hill of compacted till; steep stoss side, gentle lee side indicating ice flow. |
| Loess | Wind-blown silt deposited downwind of glacial outwash; forms fertile soils. |
| Snowball Earth | Hypothesized global glaciation when ice covered most or all of Earth.
Action Items / Next Steps (If Studying)
- Practice interpreting topographic maps for glacial features (identify moraines, eskers, drumlins).
- Relate drumlin orientations to inferred ice flow direction.
- Compare alpine vs. continental glacial landforms using map and aerial examples.
- Review fertility and formation of loess soils and their agricultural importance.