Glacial Erosion and Deposition

1. Glacial Erosion and Deposition

2. Objectives • Introduce glaciers as important agents of landscape formation, and discuss the different categories of glaciers • • Give a brief overview of how past glaciation has influenced Earth’s surface over large areas of the continents • • Describe the formation of glacier ice and its movement through the glacial system • • Explain how glaciers shape the landscape through erosion and deposition

3. Glaciers • Cryosphere • All forms of frozen water • Snow, icebergs, ice sheets, and glaciers • Glacier • Body of ice formed on land and in motion

4. Glaciers • Mountain (Alpine) Glaciers • Cirque glaciers confined to hollows below mountain peaks • Valley glaciers fill deep troughs carved into mountains • Continental Glaciers (Ice sheets) • Large landmasses covered with sheets of ice

5. Glaciers of the Past • Glacial periods • Ice sheet expansion in high to middle latitudes • Due to cooling climatic conditions • Deglaciation • Glacial retreat due to warming climate conditions • Interglacial • Warm period between glacial periods

6. Formation of Glacier Ice • Begins with snow • Summer snow loss is less than winter gain • Compacted snow • Recrystallized by melting and refreezing of ice in pore spaces • Firn • Granular, compacted snow • Not quite glacial ice • Glacial ice • Further compression and recrystallization

7. Ice Accumulation and Ablation • Zone of Accumulation • The addition of snow • Zone of Ablation • Loss of ice • Melting – phase change of a solid to a liquid • Sublimation – phase change of a solid to a gas • Calving – break up of glaciers that flow into ocean

8. Glacial Movement • Glacial Surge • Rapid movement as much as 1 m/hr • Glacial Creep • Internal deformation of ice • Glacial Sliding • Movement of the entire glacier over the rocks below

9. Glacial Movement and Temperature • Warm weather • Glaciers generally retreat • Ice at or near melting point • Melt water moves to the base • Produces basal slip • Cooler weather • Glaciers grow • Ice below freezing point • Temperatures rise toward base • Produces glacial creep

10. Glacial Erosion • Plucking • Bedrock is broken off and frozen within a glacier • Abrasion • Rock debris carried by glaciers scrapes the bedrock below • Striations • Linear gouges caused by rock debris within glaciers scratching the bedrock • Roche Moutonnee • Asymmetrical mounds caused by abrasion on one side and plucking on the leeward side