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GLACIER
- A. Large mass ice accumulates over 100-1000s years
- B. Form from the accumalation of snow
- 1.Snow compacted and recrystallized to form glacial ice
- C. Most glaciers move slowly
- D. Glaciers erode, transport, deposit large amounts of materia
- E.Glacial action is responisible for shaping landforms
- F. Glaciers cover approx. 10 percent of Earths surface today
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Types of Glaciers
- A. VALLEY GLACIERS
- 1. Form in mountanious areas move down stream valleys
- 2. all continents except Australia
- B.ICE SHEETS (continental glaciers)
- 1. Glaciers move outward in all directions from one or more centers of accumalation
- 2. found only in Antartica (thickness -14000 feet) and Greenland
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Glacial Movements
- A. ZONE OF FRACTURE- Upper150 feet of glacier
- B. ZONE OF FLOW
- 1. Glacier movement occurs
- 2.Basal Slip-glacier moves along underlying bedrock due to lubrication by meltwater
- 3. Plastic flow-ice actually flows in this zone
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Glacial Budget
- A.ZONE OF ACCUMULATION
- 1. Snow accumulation and ice formation occur here
- 2. Ice is added to the glacier
- B. ZONE OF WASTAGE
- 1. All the snow from the previous winter and glacial ice are lost
- a. melting
- b. Calving-pieces of glacier break off when glacier flows into a lake of ocean
- C. GLACIAL BUDGET
- 1. Terminus-end of valley glacier of an ice sheet
- 2. When accumulation>wastage, terminous advances
- 3.When wastage>accumulation, the terminus retreats
- 4. When accumulation=wastage, terminus remains stationary
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Glacial Erosion
- A. Plucking-pieces of bedrock freeze to bottom of glacier and pulled out as the glacier moves
- B. Abrasion-
- 1. Abrasive effect of particles transported along bottom and sides of glacier
- 2. Glacial striations- scratches made on underlying bedrock long particles moved along bottom glacier
- 3.Rock Flour
- i. Pulverized rock material (silt and clay sized) created rocks grind against each other during transport
- ii. May be picked up by wind and deposited as loess
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EROSIONAL FEATURES CREATED BY VALLEY GLACIERS
- A. U-shaped glaccial trough- valley glaciers widden, deepen, straighten stream valleys
- B. Cirques-bowl-shaped depressionas at head of glacial valley
- C. Hanging valley-
- 1.Smaller tributary glaciers cant erode their valleys as deeply as main glacier
- 2. When glaciers melt, smaller valleys are left above main main valley
- 3.Waterfalls from where water flows from hanging valleys
- D.Aretes-knifelike ridges separate glacial valleys or cirques
- E. Horns- pyramidlike peaks form in areas where three or more ciques surround peak
- F. Fjords-drowned glacial valley along coasts.
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GLACIAL DEPOSITION
- A.DRIFT- general term for sediment deposited by glaciers
- 1. Till- poorly sorted glacial material deposited when glacial ice melts
- 2. Stratified drift-glacial deposits trans and depo by meltwater
- B.MORAINES
- 1. Layers of till
- 2.Lateral moraine- material trans along sides of valley by valley glacier, forms lateral moraine when deposited
- 3. Medial Moraine-formed where two lateral moraines join in a valley glacier
- 4. End of Moraines
- a. Form at terminus of a valley glacier or ice sheet
- b.Terminal end moraine- form when terminus of a glacier is stationary
- c. Ground Moraine-layer of till deposited as glacier retreats
- d. Recessional moraine- form when the terminus of a retreating glacier becomes stationary
- C. VALLEY TRAINS AND OUTWASH PLAINS
- 1.Outwash plains-stratified drift deposited in front of ice sheet
- 2. Valley trains-stratififed drift deposited beyond terminus of valley glaciers
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Ice sheets
- A.OFTEN PRODUCE ROLLING TOPOGRAPHY
- B. FEATURES ASSOCIATED WITH RETREATING ICE SHEETS
- 1. Drumline
- a. symmetrical hills composed of till
- b. Probably molded in the zone of flow
- 2. Eskers- sinuous ridges of stratified drift deposited by meltwater flowing under the edge of glaciers
- 3. Kettles-depressions formed when a block of ice is left being by a retreating glacier and buried in drift
- 4.Braided streams
- a. Meltwater flowing frm glaciers carries large load of sediment
- b. Gravel and sand bars are deposited in the channels
- c.When water level is low, water has to flow around the bars producing a network of channels.
- 5. Terminal end and recessional moraines
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Pleistocene Epoch
- A. Pleistocene Epoch
- 1. 1.6 my -10,000 years
- 2.Ice sheets covered approximately 30 percent of Earths surface
- 3. Evidence for four glacial advances and retreats on land
- 4. Evidence from ocean floor sediment indicates at least 20 warming/cooling cycles occured
- B. EFFECTS OF GLACIATION
- 1. Sea level changes
- a. Occur when glaciers advance and retreat
- b. Sea level was about 450 feet lower than today at times during Pleistocene
- 2.Isostatic rebound
- a. Crust was depressed by weight of ice sheets
- b. When ice sheets retreated, crust slowly rebounded
- i. Some areas are still rebounding from Pleistocene glaciation
- 3.Some mammals grew to unusually large sizes
- a. Mammoths, ground sloths, Irish elk, glyptodonts, etc.
- 4.Pluvial Lakes
- a. Climates during the Pleistocene were cooler and wetter
- b. Permanent lakes formed in areas such as Death Valley
- c. Great Salk Lake is a remnant of much larger lake that formed during Pleistocene
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