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Information about Chap14_S06DW

Published on December 23, 2008

Author: aSGuest7897


Glacial Systems - Ch. 14 : THE Glacial Systems - Ch. 14 Glacial Systems : Glacial Systems Open system - flowing ice Input = snow Transformed into ice Ice flows under pressure Exit- evaporation & melting System equilibrium may shift Slide 3: Fig. 14.1. Diagram of a glacial system Balance Types of Glaciers : Types of Glaciers 2 types Valley glaciers Mountain areas Continental Glaciers Huge ice sheets Ice Flow : Ice Flow Pressure - slow deformation Shifting and rotation of grains of ice Pressure melting Displacement along slip planes Slide 7: Figure 14.6. Movement of ice through a glacier Gravity Flow lines Ice Flow : Ice Flow Movement is not uniform Extending flow Compressing flow slope Ice Flow : Ice Flow Ice is brittle Crevasses Generally form at ~right angle to flow Glacial Surges : Glacial Surges Rapid ice flow Likely caused by basal slip Water under ice Changes in pressure along path Ablation : Ablation Removal of ice from the system Melting Temperature, climate factors, surface debris on ice Streams may exist on the ice surface or subglacial Calving occurs where glaciers enter the sea Solid ice -> water vapor Erosion : Erosion Powerful agents of erosion Ice wedging Plucking pulls up loose fragments Rock abrades surface Glacial striations parallel to flow Valley Glacier Systems : Valley Glacier Systems Fill long mountain valleys - 10’s km U-shaped valleys from V-shaped fluvial valleys Valley Glacier Systems : Valley Glacier Systems Rock debris forms lateral & medial moraines Slide 17: Fig. 14.11. A valley glacier system Valley Glacier Systems : Valley Glacier Systems Glaciers produce unique geomorphic features Cirque Valley Glacier Systems : Valley Glacier Systems Glaciers produce unique geomorphic features Cirque Arete- A sharp crested ridge - cirques Horn - A sharp peak bounded by 3 or more cirques Hanging valleys - Valley Glacier Systems : Valley Glacier Systems At glacier terminus: Terminal moraines; Recessional moraines Outwash plains Calving if in water Slide 22: Figure 14.14. Valley glacier geomorphic features Part II - Continental : Part II - Continental Bear Tooth Pass Continental Glacier Systems : Continental Glacier Systems Most important glacial system Modify pre-existing landforms Cause crustal subsidence Modify drainage systems Important part of hydrologic system & climate Continental Glacier Systems : Continental Glacier Systems Ice sheets Continent-sized ice masses Antarctic ice sheet - to 4500 m thick Ice sheets - 95% of all glacier ice Antarctica & Greenland Glacial ice - 2.14% of water on Earth 77.4% of fresh water Continental Glacier Systems : Continental Glacier Systems Ice caps Covers large area Outward radial flow Ice shelves Continental Glacier Systems : Continental Glacier Systems Geomorphic features indicate past glacial coverage Till - debris that accumulates beneath and at glacier margins Drumlins Ground moraine - deposited beneath ice Eskers Varves Slide 34: Fig. 14.15. A continental glacier system Esker - Meltwater stream deposit : Esker - Meltwater stream deposit Drumlins - streamlined hills : Drumlins - streamlined hills Slide 37: Outwash plain Kettle lakes Varves - alternating light & darklake sediments : Varves - alternating light & darklake sediments Pleistocene Glaciation : Pleistocene Glaciation Global event that disrupted hydrologic cycle Began 2-3 mya Last glacial peak ~ 21,000 ya Multiple periods of glaciation -NOT 4 >100 m drop in sea level Slide 40: Pleistocene glaciation in NA Pleistocene Glaciation : Pleistocene Glaciation Modified drainage systems Much Pre-glacial drainage of NA was NE through Canada Glaciation produced the modern Mississippi - Missouri - Ohio river system Pleistocene Glaciation : Pleistocene Glaciation Created numerous lakes Ice scours bedrock Large lakes along margins Moraines plug valleys Pre-existing structures allow deep scouring - Great Lakes Slide 47: Fig. 14.30. Evolution of the Great Lakes Pleistocene Glaciation : Pleistocene Glaciation Sea level change Repeated rise and fall - glacial and interglacial periods Ice trapped huge quantities of water Antarctic ice sheet -melt would raise sea level ~70 m Pleistocene Glaciation : Pleistocene Glaciation Pluvial lakes In areas now arid & semi-arid regions Evidenced by remaining shoreline features and salt flats Lake Bonneville -> Great Salt Lake Chronology of glaciation : Chronology of glaciation Pleistocene Glaciation : Pleistocene Glaciation Isostatic adjustment Ice sheets - depression of lithosphere Continue rebound post glaciation Rebound rates - to 3.5 cm/yr still occur Pleistocene Glaciation : Pleistocene Glaciation Ocean waters cooled Changes in ocean chemistry Altered ocean circulation Ice rafted sediments accumulated on the ocean floor Impacts world-wide Pleistocene Glaciation : Pleistocene Glaciation Severe climate change shifted ecology Plants died - animals migrated Species displaced ~ 3200 km New migration routes - lower sea level Areas covered by ice depopulated Numerous extinctions Especially large mammals Slide 58: Fig 14.38. Glacial periods Other glacial periods Causes of Glaciation : Causes of Glaciation Glaciation an unusual event Earth’s climate generally milder than today Location of continents a factor Causes of Glaciation : Causes of Glaciation Causes of climate change Milankovitch cycles - changes orbit and axis tilt Late Cenozoic evidence supports this Changes in atmospheric composition Position of continents and ocean circulation Continuing climatic change : Continuing climatic change The End : The End

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