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GLACIERS AND GLACIATION

GLACIERS AND GLACIATION. GLACIER. A body of ice Formed on land Recrystallization of snow=> Firn => Ice Evidence of movement Alpine (valley) glaciation Continental glaciation. Ice Ages. Northern Europe & North America heavily glaciated Pleistocene 1.8 million years BP to 10,000 ybp

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GLACIERS AND GLACIATION

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  1. GLACIERSAND GLACIATION

  2. GLACIER • A body of ice • Formed on land • Recrystallization of snow=> Firn => Ice • Evidence of movement • Alpine (valley) glaciation • Continental glaciation

  3. Ice Ages • Northern Europe & North America heavily glaciated • Pleistocene 1.8 million years BP to 10,000 ybp • 4 episodes • Peak of glaciation (Wisconsin) 18,000 years ago

  4. Glaciers-Where they are • Develop where all of annual snow doesn’t melt away in warm seasons: • Accumulation rate rate exceeds ablation (melting) rate • Polar regions • Heavy winter snowfall • High elevations • 85% in Antarctica • 10% in Greenland

  5. Types of Glaciers • Valley or Alpine glacier • Ice sheet • Continental Glaciers

  6. GLACIERS • Wastage of glaciers (“shrinkage”) • Melting • more melting at lower elevations • Evaporation • Calving into Icebergs • where a glacier flows onto a sea

  7. Movement of Glaciers • Valley Glaciers • Gravity driving force • Sliding along its base -basal sliding • Internal flowage- plastic flow • Rigid zone • Crevasses may form here • Ice sheets • Move downward & outward from central high

  8. Glacial Erosion • Under glacier • Abrasion & plucking • Bedrock polished & striated • Rock flour washes out of glacier • Polishing and rounding • “Sheep Rocks” • Striations- scratches & grooves on rock • Above glacier • Frost wedging takes place • Erosion by glaciers steepens slopes

  9. Erosional Landscapes Associated with Alpine Glaciation • Glacial valleys • U-shaped valleys • Hanging valleys • Rock -basin lakes (tarns) • Rounded knobs- rouche moutonnees

  10. Erosional Landscapes Associated with Alpine Glaciation • Cirque- at head of valley glacier • Rock steps • Rock basin lakes • Horn • Arete- sharp ridge

  11. Erosional Landscapes Associated with Continental Glaciation • Grooved and striated bedrock • Grooves may be channels • Rounded hills & mountains

  12. Glacial Deposition • Till • Unsorted debris (Boulders to Clay) • Erratic- Large Boulders moved from far away • Moraine- body of till • Lateral Moraine • Medial Moraine- where tributaries join • End moraine- • Terminal • Recessional • Drumlin

  13. Glacial Deposition • Outwash • Stream-deposited sediment • sorted • Braided streams typical • Esker • Kettle

  14. Effects of Past Glaciation • Glacial ages • Direct effects in North America • Scoured much of Canada • Cut Great Lakes • Deposited till & flattened Midwest • Extensive alpine glaciation in mountains

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