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GLACIERS AND GLACIATION I. Topics. Intro Glaciers and the Hydrologic cycle Types Movement Glacial landforms Glacial erosion Glacial sedimentation Glacial lakes Glaciations and global climate. GLACIER. A large body of moving ice Formed on land Recrystallization of snow Types:
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Topics • Intro • Glaciers and the Hydrologic cycle • Types • Movement • Glacial landforms • Glacial erosion • Glacial sedimentation • Glacial lakes • Glaciations and global climate
GLACIER • A large body of moving ice • Formed on land • Recrystallization of snow • Types: • Alpine (valley) glaciers • Continental glaciers
Valley Glaciers in Denali National Park Courtesy USGS
Glaciers-Where they are • Develop where all of annual snow doesn’t melt away in summer • Polar regions • Heavy winter snowfall • High elevations • 85% in Antarctica • 10% in Greenland
Types of Glaciers • Valley glacier • Continental Glaciers: • Ice sheets (big) • Ice cap (small)
Greenland Ice Sheet:contours indicate elevation of ice sheet above sea level Fig. 12.5
Formation and Growth of Glaciers • Metamorphism of Snow • Glacial Budgets • Zone of accumulation • Zone of wastage • Snow line- divides the zones • Negative budget- Receding glacier • Positive budget- Advancing glacier • Terminus- movement reflects budget
GLACIERS • Wastage of glaciers (“shrinkage”) • Melting • more melting at lower elevations • Evaporation • Calving into Icebergs • where a glacier flows onto a sea
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
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
Erosional Landscapes Associated with Alpine Glaciation • Glacial valleys • U-shaped valleys • Hanging valleys • Truncated spurs • Triangular facets • Rock -basin lakes (tarns) • Rounded knobs- rouche moutonnees
Erosional Landscapes Associated with Alpine Glaciation • Cirque- at head of valley glacier • Rock steps • Rock basin lakes • Horn • Arete- sharp ridge
Erosional Landscapes Associated with Continental Glaciation • Grooved and striated bedrock • Grooves may be channels • Rounded hills & mountains
Glacial Deposition • Till • Unsorted debris • Erratic • Moraine- body of till • Lateral Moraine • Medial Moraine- where tributaries join • End moraine- • Terminal • Recessional
Other Glacial Landforms • Drumlins- • Elongated hills of glacial till • Point down-glacier • Eskers • Sinuous ridges of stratified till • Form in tunnels under the ice sheet • Some times 100km long or more
Glacial Deposition • Outwash • Stream-deposited sediment • sorted • Braided streams typical • Esker • Kettle • Glacial lakes
Glacial Lakes • Pluvial Lakes- • Due to wetter climate • Examples: Lake Bonneville, Death Valley • Lake Bonneville flood into Snake River Canyon • Proglacial Lakes • In front of the glacial sheet • Ice dammed lakes • Examples: Great Lakes, Lake Missoula
Lake Bonneville Flood • The lake was up to 1000 feet deep • A ridge on the north side gave way • Peak flow 33 million cubic feet/second • 33 MCF would fill in a tanker train 165 miles long • A raft would move at 75 mph on a wave 300 ft high • Flood left behind giant ripples