Glacial Erosion and Deposition

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

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

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

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

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

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

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

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

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