Glaciers: Formation, Movement, Erosion, and Impact

Chapter 6 - Glaciers

Glacier Formation

Describe how glaciers form (using the terms zone of accumulation and zone of ablation).

Zone of Accumulation

• The area where a glacier forms.
• More snow falls in winter than melts in summer.

Zone of Wastage

• The area where there is a net loss due to melting.

Zone of Fracture

• Uppermost 50 meters.
• Crevasses form in brittle ice in this zone.

What part of the glacier behaves brittly? Plastically?

Types of Glacial Movements

• Plastic flow
• Slipping along the ground below 50 meters

Brittly in the picture

Valley Glaciers vs. Continental Glaciers

What are valley glaciers? Continental glaciers? Examples of each.

1. Valley, or alpine glaciers – form in mountainous areas
2. Ice sheets, or continental glaciers
   • Large scale e.g., Over Greenland and Antarctica

Picture

Glacial Erosion Features

Know the types & definitions of each.

Landforms Created by Glacial Erosion

• Glacial trough
• Hanging valley
• Cirque
• Arête
• Horn
• Fiord

Basin and Range Evolution

Basin and Range: the evolution of a desert landscape

• Erosion of mountain mass causes local relief to continually diminish, erode.
• Eventually mountains are reduced to a few large bedrock knobs called inselbergs projecting above a sediment-filled basin.

Wind Erosion

• Deflation
  • Lifting of loose material
  • Produces
    • Blowouts
    • Desert pavement
• Abrasion

Glacial Depositional Features

Know the types & definitions of each.

Depositional Features

• Moraines – layers or ridges of till
  • Types of moraines
    • Lateral
    • Medial
    • End
    • Ground

Other Depositional Features

• Outwash plain, or valley train
• Kettles
• Drumlins
• Eskers
• Kames

Pleistocene Glaciation (Ice Age)

What was the geographic extent of glaciers in the last ice age (Pleistocene glaciation)?

Ice Age (most recent)

• Began 2 to 3 million years ago
• Division of geological time is called the Pleistocene epoch
• Ice covered 30 percent of Earth’s land area

What happened to the base level of rivers when glaciers formed? Melted?

Rebounding of the Crust

Rebounding upward of the crust after glaciers melt

• Can cause earthquakes in areas far from plate edges (i.e. Virginia)
• Worldwide change in sea level
• Change in base level of rivers

Climatic Changes

• Migration of animals and plants
• Pluvial Lakes – form in deserts during ice ages (cooler, wetter conditions)

Causes of Glaciations

What are causes of glaciations?

• Successful theory must account for
  • Cooling of Earth, as well as
  • Short-term climatic changes
• Proposed possible causes
  • Plate tectonics
    • Continents were arranged differently
    • Changes in oceanic circulation result affecting global heat distribution

Astronomical Causes

• Variations in Earth’s orbit
• Milankovitch hypothesis
  • Shape (eccentricity) of Earth’s orbit varies
  • Angle of Earth’s axis (obliquity) changes
  • Axis wobbles (precession)
  • Changes in climate over the past several hundred thousand years are closely associated with variations in Earth’s orbit

Effects of Glaciations

Effects of glaciations?

Rebounding of the Crust

Rebounding upward of the crust after glaciers melt

• Can cause earthquakes in areas far from plate edges (i.e. Virginia)
• Worldwide change in sea level
• Change in base level of rivers

Climatic Changes

• Migration of animals and plants
• Pluvial Lakes – form in deserts during ice ages (cooler, wetter conditions)