Chapter 15: Glaciers and Glaciation

OBJECTIVES• Explain the formation and movement of glacier ice.

• Describe the process of glacial erosion and the landforms that glacial erosion produces.

• Describe the processes of glacial deposition and the effects glaciers have on Earth’s landscape.

• Describe the influence of the Pleistocene ice age on the landscapes of the northern hemisphere.

OBJECTIVES• Summarize the evidence that is used to deduce the

existence and causes of ancient ice ages.

• List other instances of glaciation from across our Solar System.

• A glacier forms on land and is heavy enough to flow under its own weight.

• Firn, a granular variety of ice, forms when snow crystals are compacted.

• As firn is compressed, it forms glacial ice.

Glacial Ice

Fig. 15.1

• Glaciers grow when accumulation exceeds ablation.

• Glaciers shrink when ablation exceeds accumulation.

Glacial Growth

Fig. 15.6

Types of Glaciers• Continental glaciers cover an entire landmass.

• Alpine glaciers form at high altitudes.

Figs. 15.3a, Fig 15.4

• Plastic flow occurs when ice crystals change shape.

• Basal sliding occurs when the glacier slides along its base.

How Glaciers Move

Fig. 15.5

• Continental glaciers produce striations as well as roches moutonées.

Continental Glacial Erosion

Striations Roche moutonéeFigs. 15.7, 15.8

• Erosion by alpine glaciers produces a variety of landforms.

Alpine Glacial Erosion

Fig. 15.10

• Glaciers transport large amounts of sediment.• Glacial sediment can be deposited by ice or meltwater.• Sediment deposited by a glacier is known as glacial drift.

Glacial Deposition

Fig. 15.17

Types of Moraines

Figs. 15.19, 15.20

• Stratified drift, outwash plains, kettles, kames, and eskersform as a result of glaciers melting.

Meltwater Deposits

Fig. 15.24

• During the Pleistocene Epoch, glaciers covered much of North America.

• The Pleistocene ice age had effects on sea level and topography.

The Pleistocene Ice Age

Fig. 15.28

• Pluvial lakes form as a result of increased precipitation and reduced evaporation.

• Some modern landforms in the southwest United States are former pluvial lakes.

Pluvial Lakes

Fig. 15.29

• The Pleistocene glaciation significantly changed drainage in most of North America.

Glacial Modification of Drainage

Fig. 15.32

• Continental positions and plate tectonic motions can affect global climate and lead to glaciation.

Plate Tectonics and Glaciation

Fig. 15.37

• A number of other bodies in the Solar System, including Europa and Mars, have ice on or below the surface.

Ice on Other Worlds

Figs. 15.39a, 15.40

Summary• Glaciers

• Form when snow becomes compacted and begins to flow under its own weight

• Move via plastic flow and basal sliding• Can produce distinctive landforms through erosion and

deposition• Covered a much larger portion of Earth’s surface during

the Pleistocene Epoch• Produced many of the distinctive topographic features

in North America• May be found on other bodies in the Solar System in

addition to Earth