Ch. 11 - Glaciers
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Transcript of Ch. 11 - Glaciers
![Page 1: Ch. 11 - Glaciers](https://reader036.fdocuments.in/reader036/viewer/2022062312/55575976d8b42a63448b511e/html5/thumbnails/1.jpg)
Glaciers
Ch. 11
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Glaciers
Thick mass of ice
- accumulates on land
- flows downhill
- caused by large snowfalls in winter and ____________
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Types of Glaciers
1) Valley (alpine)
- smallest glaciers
- occupy valleys formerly carved by streams
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Types of Glaciers
2) Piedmont
“pied” = French for “foot”
- valley glaciers coalesce at base of steep mountain front
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Types of Glaciers
3) Ice caps- cover upland & plateau areas- not confined to valleys- smaller in extent than ice sheetsEx: Iceland
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Types of Glaciers
4) Ice Sheets
- largest glaciers
- cover continental regions
- today: Greenland & Antarctica
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Ice sheets
- several 1000’s feet thick
- flow outward from central high spot
- covers all but highest elevations
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Ice shelves
Occur where ice sheets flow into oceans
- large flat masses of ice attached to land by one or more sides
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Glaciers:
Sediment Transport:
High capacity –
High competency –
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Erosion Methods
1) Plucking – meltwater gets into cracks in bedrock & freezes
- pieces incorporated into base of ice (worn flat on one side)
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Striations
Scratches in exposed bedrock
- indicate direction of glacial movement
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Erosion Methods
2) Abrasion
- weight of moving rx & ice scrapes bedrock
- occurs at point of contact
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Erosional Landscapes
Valley glaciers produce jagged mountain scenery
Ex: Rocky Mountains
Ice sheets smooth out landscape
Ex: Peoria area
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Erosional Landscapes
1) Glacial trough (U-shaped cross-section)
Ice widens, deepens, & straightens former stream valleys
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Erosional Landscapes
2) Hanging valley
- smaller valley from a tributary glacier is left higher than main valley
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Erosional Landscapes
3) Cirque (“circle”)
- occurs at head of glacial trough
- steep walls around 3 sides but opens on 4th side
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Erosional Landscapes
4) Horn
Sharp pyramid-shaped peak
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Erosional Landscapes
5) Arete
Knife-like ridge separating adjacent glacial troughs
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Erosional Landscapes
6) Tarn – lake occupying a cirque after glaciers melt
7) Paternoster lakes
- series of lakes that sit in glacial trough
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Erosional Landscapes
8) Fiord
Drowned glacial trough after last Ice Age passed
Occur where mtns. are adjacent to oceans at high latitudes
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Depositional Landscapes
Glacial drift = all sediment deposited by glaciers
Two types of drift:
a) Till = sediment deposited directly by glaciers (unsorted)
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Two types of drift:
b) Stratified drift = sediments deposited by glacial meltwater
- sorted by size
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Landforms composed of till
1) Erratic
- boulders that differ from underlying bedrock
- source area is outside region where they’re found
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Landforms composed of till
2) Moraine – ridge of till
Several types:
a) Lateral moraine – found only w/ valley glaciers
- parallels sides of valley
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Lateral Moraine
Material comes from:
a) ice scraping valley walls
b) rx from cliffs above
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Types of Moraines
b) Medial moraine
- lateral moraines from joining glaciers merge
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Types of Moraines
c) End moraine
- associated w/ stationary glaciers
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Types of Moraines
d) Recessional moraines
- end moraines created as a receding glacier occasionally stabilized
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Types of Moraines
e) Terminal moraine
- outermost end moraine that marks limit of glacial advance
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Types of Moraines
f) Ground moraine
- associated w/ receding glaciers
- forms behind end moraines
- acts to level the land
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Landforms composed of stratified drift
Deposited by glacier’s melt water
- flows through moraines & picks up sediment
- braided stream channels common
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Landforms composed of stratified drift
1) Outwash plains
- broad ramp-like surface built in front of end moraines
- associated w/ ice sheets
(called “valley trains” w/valley glaciers)
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Landforms composed of stratified drift
2) Kettle/kettle lakes
- large blocks of stagnant ice buried in sediment
- ice melts
- creates a depression
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Depositional LandformsLoess
- windblown silt deposits
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Loess
- associated with meltwater drainages from glaciation
- thickest near drainages and thins away from valleys
![Page 36: Ch. 11 - Glaciers](https://reader036.fdocuments.in/reader036/viewer/2022062312/55575976d8b42a63448b511e/html5/thumbnails/36.jpg)
Movement of a glacier
Two methods:1) Plastic flow = internal flow- occurs in ice below 50 meters- occurs fastest in center of glacier
(less friction)
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Zone of Fracture
Upper 50 meters of glacier
- brittle
- breaks into cracks called “crevasses”
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Movement of a glacier
2) Basal slip
Melt water at base of glacier
- entire ice mass slips over surface
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Glacial Budgets
Zone of Accumulation = area where snow accumulates & ice forms
Zone of Wastage = net loss as glacier advances into warmer climates (lower elevations)
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Zone of Wastage
Loss of snow & ice is called ablation
Ablation is due to:
- melting
- calving
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Glacial Budgets
Snowline = boundary between zone of accumulation & zone of wastage
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Glacial Budgets
1) Advancing glacier – more accumulation than ablation
- glacial front advances
- snowline drops in elevation
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Glacial Budgets
2) Retreating glacier
- ablation exceeds accumulation
- snowline rises in elevation
- caused by warming trend or decrease in snowfall
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Glacial Budgets
3) Stationary Budget
- accumulation equals ablation
- total area of glacier is not changing
NOTE: Ice is always moving downhill!
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Evidence for past glacial periods (“Ice Ages”)
Periodically, northern Europe & N. America covered by great ice sheets
Last one melted from Canada <10,000 years ago
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Evidence for past glacial periods (“Ice Ages”)
1) Glacial erosion
Ice sheets: polished bedrock in northern regions, striations, recessional moraines
Ex: Central Park, New York City
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Evidence for past glacial periods (“Ice Ages”)
Valley glaciers:
- Yosemite National Park
- Yellowstone National Park
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Yosemite
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Evidence for past glacial periods (“Ice Ages”)
2) Pluvial lakes
- form during cooler times w/ moderate rainfall
- occurred at lower latitudes where ice did not advance
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Pluvial lakes
Most evident in Basin & Range region in western U.S.
Ex: Lake Manley, Death Valley
Ex: Lake Bonneville, Utah
(Great Salt Lake is a remnant)
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Evidence for past glacial periods (“Ice Ages”)
3) Decreasing sea level
Water is locked onto land by ice
Estimated maximum 100 meters lower than present sea level
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Decreasing sea level
Evidence:Submerged stream channels on
continental shelves
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Evidence for past glacial periods (“Ice Ages”)
4) Crustal Rebound
Land readjusts upward after ice sheets melt
Hudson Bay region has uplifted 300 meters since end of last ice age
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Crustal rebound
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Evidence for past glacial periods (“Ice Ages”)
5) Lake Missoula
Ice dam blocked melt water
- formed huge lake that flooded western Montana
(half the size of Lake Michigan)
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Lake Missoula Map
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Lake Missoula
Melting weakened ice dam
- lake emptied in 1-2 days
- discharge ~ 386 million cfs (Amazon discharge = 6 million cfs)
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Lake Missoula
Evidence:a) channeled scablands in western
Oregon & southern Idahob) giant ripples of coarse gravel
30’ high, 300’ apart, 2 miles long