Cold Climate Glaciers and Ice Ages

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• Cold Climate - Glaciers and Ice Ages

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Glaciers

• Glacier a large, long-lasting mass of ice,
  formed on land that moves under the influence of
  gravity and its own weight
  
• Glaciers form by accumulation and compaction of
  snow
  
• Packed snow becomes firn
• Then refreezes to ice

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Formation of Glacial Ice from Snow
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Glaciation Types

• Alpine glaciation found in mountainous regions
• Continental glaciation exists where a large part
  of a continent is covered by glacial ice
  
• Cover vast areas

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Davidson Glacier near Haines, AlaskaAn Alpine
glacier system
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Types of Glaciers
Alpine
Continental
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Alpine Glaciers

• Are confined by surrounding mountains
• Types
• Cirque Glaciers erode basins in mountainsides
• Valley Glaciers flow into preexisting stream
  valleys
  
• Icecaps form on mountaintops

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Types of Glaciers Cirque Glacier
Mount Edith Cavell, Jasper National Park, Canada
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Types of Glaciers Valley Glacier
Tongas National Forest, Alaska
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Types of Glaciers Icecap and Continental
http//www.nmm.ac.uk/server/show/conWebDoc.1221
Sentinal Range, Antarctica
Antarctica is the broadest high place on Earth,
the ice cap is up to 4km thick
and covers the continent Antarctica is a desert,
with only 15 cm (6 inches) of snowfall a year
around the South Pole The lowest recorded tempe
rature is -89.2 C. There is no life in Antarctic
a except near the coast
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Types of Glaciers Piedmont Tidewater
Piedmont Originally confined alpine, spread at
foot of mountains
Source Jim Wark/Peter Arnold, Inc.
Calving
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Iceberg Calving Hubbard Glacier, Wrangell-St.
Elias National Park, Alaska
Releases fresh water to oceans, CO2 to
atmosphere.
More on this later.
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A Glaciers Budget

• Budget Gain Loss
• Gains snow in zone of accumulation
• Loses ice in zone of ablation
• Budget can be positive (net growth)
• Static
• or negative (net melting)

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A Glaciers Budget
Year round Snow
Summer Rain
Note that a glacier is a river. Even if the
terminus doesnt advance, still flows
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Glacial Flow

• Internal deformation
• Ice crystals slide past one another
• Basal Sliding
• Entire glacier slides downhill on a thin film of
  meltwater at its base.
  
• Glacier always flows toward zone of ablation

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Mechanics of Glacial Flow
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Erosion by Glaciers

• Abrasion
• Rocks embedded in glaciers base make linear
  scratches and grooves in bedrock
  
• Quarrying
• Glacier breaks off and removes large blocks of
  rock. FROST WEDGING is important
  

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Glacial Abrasion in Bedrock
Source Tom Bean
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Glacial Erosion Roche Moutonée
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Glacial Erosion Roche Moutonée
Yosemite NP, Calif
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Erosion by Glaciers (cont.)

• Alpine glaciers erode mountain slopes into
  horseshoe shaped basins called cirques
  
• Melting forms cirque lake (tarn)
• Erosion of two or more cirques erodes intervening
  rock
  
• Horns pointy peaks made by trios
• Arêtes long serrated ridges by pairs
• Cols passes through the arêtes

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Alpine Glacial Erosion
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Alpine Glacial Erosion
Origin of Hanging Valley
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Yosemite Falls
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Valley Glaciers

• Erode a large quantity of bedrock and sediment
• Convert V-shaped stream valleys into U-shaped
  glacial valleys.

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U-Shaped Valley in Tracy Wilderness, Southeastern
Alaska
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Seawater Flooded U-Shaped Valleys Fjords
Bela Bela Fjord, BC
When glaciers melt, sea-level rises
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Erosion by Continental Glaciation

• Erosional Landforms much larger in scale than
  alpine glaciers
  
• Whalebacks huge Roche Moutonée
• Huge U-shaped troughs
• Finger Lakes, Great Lakes, Puget Sound, Loch
  Ness were all once stream valleys excavated by
  Ice Sheets

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Erosion of Preglacial Lowlands (Finger Lakes)
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Erosion of Lowlands (Great Lakes, Finger Lakes)
Superior
Huron
Michigan
Ontario
Erie
Source U.S. Dept. of Interior, USGS Eros Date
Center
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Glacial Deposits - Drift

• Collectively called Glacial Drift
• TYPE 1 UNSORTED
• Glacial Till unsorted, unstratified sediments
  deposited by melting ice.
  
• May contain glacial erratics
• Often accumulates in glaciers channel and at its
  terminus as a Moraine
  
• Terminal Moraine hills of sediment left by a
  glaciers retreat.
  
• Terminal Moraines may be reshaped by a later
  glacial advance into Drumlins rounded elongated
  hills perpendicular to their original orientation

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Advance Retreat Moraines
Note moraine, retreat or stationary

Stationary Analogy Escalator
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Stationary Retreat Moraine at Terminus
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Large Granite Erratics
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Lateral and Medial Moraines
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Lateral and Medial Moraines Kennicott Glacier
Wrangell-St. Elias NP, SE AK
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The Origin of Drumlins
Glacier retreats, leaving behind
a terminal moraine. Later it advances again, and
reshapes the moraine into a drumlin.
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Drumlins Rochester,NY
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Glacial Deposits - Drift

• TYPE 2 SORTED
• Outwash sorted stratified sediments deposited by
  meltwater streams
  
• Loess wind erosion of drying outwash silt.
• Eskers sinuous meltwater deposits of sand and
  gravel underneath ice
  

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Origin of Eskers
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Eskers in Coteau des Prairies, South Dakota
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Effects of Glaciation

• Change Climate increase precipitation
• locally - pluvial lakes
• Depress continents lateral rebound
• Drop sea-level alter coastlines
• Form continent-wide Dams
• Divert streams Ohio and Missouri rivers

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Formation of Terraces due to Crustal Rebound
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Lowered Sea-level - Landbridge
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Glacier Distribution 20,000 ya
Approximate Maximum
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Lowered Sea-level exposed continental shelf
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The Creation of Glacial Lake Missoula
Purcell Lobe blocks Clark Fork River
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The Draining of Glacial Lake Missoula
Repeated many times, last time 13000 kya
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Giant Ripples of the Missoula Flooding
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Causes of Ice Ages

• Plate Tectonics
• Moves Continents to Poles
• Raises mountains above snowline
• Orbit distance, Axis Tilt and Wobble
• Moderates solar radiation north of 65 N
• Milankovitch Cycles 100,000 years
• Low summertime radiation 65 N, glaciers expand

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Milankovitch Cycles
Discussion cool summers and wet winters
Moisture content of air masses
100,000 years
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Warm Wet Winter Cool Summer
Cold Dry Winter Hot Summer
41,000 years
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Discussion Perihelion and Aphelion
25,700 years
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One More Point On This

• The orbital affects that Milankovitch suggested
  as a partial cause for ice ages each have a
  different period.
  
• They combine at irregular intervals
• The average is about 100,000 years
• but that is ONLY an average

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Earths Past Ice Ages(oldest on bottom)

• Tertiary- Quaternary cooling Pleistocene 1.8
  mya
  
• None in Mesozoic
• Late Pennsylvanian Permian Ice covered part
  Gondwana (South Africa, South America, India,
  Australia, Antarctica)
  
• Ordovician glaciation
• Area that is now the Sahara at South Pole
• PreCambrian Tillites (Lithified Till)
• At least three episodes. Interesting
  examples
  
• 750 mya ice from poles to tropic SNOWBALL
  EARTH
  
• Oldest 2.8 bya

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Permian Glaciation Gondwana Tillites
Poorly Sorted Unstratified
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Cenozoic Cooling
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The Late Tertiary and Quaternary oxygen isotope
record measured in marine fossil shells
Evap. water and CO2 during glacial time
removes 16O to glacier ice leaving
18O in oceans for CaCO3 shell
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Pleistocene Glaciation

• Since 1.6 mya more than 30 advances and
  retreats
  
• In 4 large scale pulses.
• Latest retreat 10,000 years ago Laurentide
• Little ice age 700 to 150 years ago.
• Sustained warming since 1850

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Foraminifera tests - Ice Age
Wisconsinan
Illinoian
30 pulses in 4 or so major groups
Kansan
Nebraskan
Evap. water and CO2 during
glacial removes 16O to
glacier ice leaving 18O in oceans
for CaCO3 shell
warm
cold
Also spiral direction diversity dep T
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Continuous Ice Sheet 20 kya then warming
Scoured 30 M below sea-level
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Cold pulse from about 1300 to 1850 AD (The
so-called Little Ice Age)Climate has been
warming since then.
Discussion Global Warming
Worldwide melting, regardless of cause, releases
CO2 and H2O and exposes dark land. The atmosphere
receives and holds more heat, and temperature
rise.
Athabaska Glacier, Columbia Icefield, W. Canada
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End of Glaciers