Glaciers

Glaciers: Glacier – a thick mass of ice that forms over land from the compaction and recrystallization of snow and shows evidence of past or present flow

Types of glaciers Valley/mountain/alpine glaciers – form in mountainous areas Ice sheets or continental glaciers Large scale e.g., Over Greenland and Antarctica Ice Caps: Small Ice sheets

Currently ice sheets cover Greenland and Antarctica

Movement of glacial ice Types of glacial movements Plastic flow Slipping along the ground Zone of fracture Uppermost 50 meters Crevasses form in brittle ice

Movement of glacial ice Zone of accumulation – the area where a glacier forms Zone of wastage – the area where there is a net loss due to melting

Accumulation and Wastage Figure 6.7

Glacial Erosion Plucking – Gouging out and lifting of chunks of rocks Abrasion Striations (scratches and grooves in the bedrock)

Landforms created by glacial erosion Glacial trough Hanging valley Cirque Arête Horn Fjord

Erosional landforms created by alpine glaciers

The Matterhorn in the Swiss Alps

Glacial deposits Glacial drift Till – material that is deposited directly by ice Stratified drift – sediment deposited by water melting off surface of glacier

Glacial till is typically unstratified and unsorted Figure 6.13

Close-up view of the boulder in the previous slide

Glacial deposits Depositional features Moraines – layers or ridges of till Types of moraines Lateral Medial End Ground

Glacial deposits Depositional features Outwash plain or valley train Kettles Drumlins Eskers Kames

Glacial depositional features

Kettle lakes

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

Maximum extent of ice during the Ice Age Figure 6.22

Indirect effects of Ice Age glaciers Migration of animals and plants Rebounding of the crust Drop in sea level Climatic changes

Causes of glaciation Variations in Earth’s orbit Shape of Earth’s orbit varies Angle of Earth’s axis changes Axis wobbles