GLACIERS AND GLACIATION I

1. GLACIERSAND GLACIATIONI

2. Topics • Intro • Glaciers and the Hydrologic cycle • Types • Movement • Glacial landforms • Glacial erosion • Glacial sedimentation • Glacial lakes • Glaciations and global climate

3. GLACIER • A large body of moving ice • Formed on land • Recrystallization of snow • Types: • Alpine (valley) glaciers • Continental glaciers

4. Winter Sea Ice- Beaufort Sea

5. Sea Ice- Bering Sea

6. Timble Glacier, Alaska

8. Valley Glaciers in Denali National Park Courtesy USGS

9. Hydrologic Cycle - 2% of water is Ice

10. What if the glaciers melt?

11. 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

12. Types of Glaciers • Valley glacier • Continental Glaciers: • Ice sheets (big) • Ice cap (small)

16. Greenland Ice Sheet:contours indicate elevation of ice sheet above sea level Fig. 12.5

18. Ross Ice Shelf, Antartica

20. 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

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

23. 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

25. 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

28. 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

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

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

37. Glacial Deposition • Till • Unsorted debris • Erratic • Moraine- body of till • Lateral Moraine • Medial Moraine- where tributaries join • End moraine- • Terminal • Recessional

40. Erratic-Alberta, Canada

41. 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

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

45. 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

47. Lake Bonneville- 14,000 yrs ago- Utah

48. 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