Systems Glacial - Ch. 14
THE
Glacial Systems
Open system - flowing ice
Input = snow Transformed into ice Ice flows under pressure Exit- evaporation & melting System equilibrium may shift
Balance
Fig. 14.1. Diagram of a glacial system
QuickTime and a Video decompressor are needed to see this picture.
Types of Glaciers
2 types
Valley glaciers
Mountain areas
Continental Glaciers
Huge ice sheets
Ice Flow
Pressure - slow deformation Shifting and rotation of grains of ice
Pressure melting Displacement along slip planes
Gravity Flow lines
Figure 14.6. Movement of ice through a glacier
Ice Flow
Movement is not uniform
Extending flow Compressing flow slope
Ice is brittle
Crevasses
Ice Flow
Generally form at ~right angle to flow
Glacial Surges
Rapid ice flow
Likely caused by basal slip
Water under ice
Changes in pressure along path
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
Powerful agents of erosion
Ice wedging
Plucking pulls up loose fragments
Rock abrades surface
Glacial striations parallel to flow
Valley Glacier Systems
Fill long mountain valleys - 10's km U-shaped valleys from V-shaped fluvial valleys
Valley Glacier Systems
Rock debris forms lateral & medial moraines
Fig. 14.11. A valley glacier system
Valley Glacier Systems
Glaciers produce unique geomorphic features
Cirque
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
At glacier terminus:
Terminal moraines; Recessional moraines Outwash plains Calving if in water
Figure 14.14. Valley glacier geomorphic features
QuickTime< and a Video decompressor are needed to see this picture.
QuickTime and a Video decompressor are needed to see this picture.
Bear Tooth Pass
Part II Continental
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
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 Ice caps
Covers large area Outward radial flow
Ice shelves
Continental Glacier Systems
Geomorphic features indicate glacial past coverage Till - debris that accumulates beneath and at glacier margins
Drumlins Ground moraine - deposited beneath ice
Eskers Varves
Fig. 14.15. A continental glacier system
Esker - Meltwater stream deposit
Drumlins - streamlined hills
Outwash plain
Kettle lakes
Varves - alternating light & dark lake sediments
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
Pleistocene glaciation in NA
QuickTimeOE and a Photo decompressor are needed to see this picture.
QuickTime and a Photo decompressor are needed to see this picture.
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
Created numerous lakes
Ice scours bedrock Large lakes along margins Moraines plug valleys Pre-existing structures allow deep scouring - Great Lakes
Fig. 14.30. Evolution of the Great Lakes
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
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
Pleistocene Glaciation
Isostatic adjustment
Ice sheets - depression of lithosphere Continue ...