Cold Climate - Glaciers and Ice Ages

GlaciersGlaciers

• Glacier: a large, long-lasting mass of ice, Glacier: a large, long-lasting mass of ice, formed on land that moves under the formed on land that moves under the influence of gravity and its own weight influence of gravity and its own weight

• Glaciers form by accumulation and Glaciers form by accumulation and compaction of snowcompaction of snow– Packed snow becomes Packed snow becomes firnfirn

– Then refreezes to iceThen refreezes to ice

Formation of Glacial Ice from SnowFormation of Glacial Ice from Snow

Glaciation TypesGlaciation Types

• Alpine glaciation: found in mountainous Alpine glaciation: found in mountainous regions regions

• Continental glaciation: exists where a Continental glaciation: exists where a large part of a continent is covered by large part of a continent is covered by glacial iceglacial ice

Cover vast areas

Davidson Davidson Glacier near Glacier near Haines, Haines, AlaskaAlaska

An Alpine An Alpine glacier glacier systemsystem

Types of GlaciersTypes of Glaciers

Alpine Continental

Alpine GlaciersAlpine Glaciers

• Are confined by surrounding mountains

Types:

• Cirque Glaciers – erode basins in mountainsides

• Valley Glaciers – flow into preexisting stream valleys

• Icecaps – form on mountaintops

Types of GlaciersTypes of Glaciers– Cirque Glacier– Cirque Glacier

Mount Edith Cavell, Jasper National Park, Canada

Types of Glaciers Types of Glaciers – Valley Glacier– Valley Glacier

Tongas National Forest, Alaska

Types of Glaciers Types of Glaciers – Icecap and Continental– Icecap and Continental

Sentinal Range, Antarctica

http://www.nmm.ac.uk/server/show/conWebDoc.1221

•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 temperature is -89.2 °C.•There is no life in Antarctica except near the coast

Types of Glaciers Types of Glaciers – Piedmont & Tidewater– Piedmont & Tidewater

Source: Jim Wark/Peter Arnold, Inc.

Piedmont: Originally confined alpine, spread at foot of mountains

Calving

Iceberg Calving Iceberg Calving – – Hubbard Glacier, Wrangell-St. Elias National Park, AlaskaHubbard Glacier, Wrangell-St. Elias National Park, Alaska

Releases fresh water to

oceans, CO2 to atmosphere.

More on this later.

A Glacier’s BudgetA Glacier’s 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)

A Glacier’s BudgetA Glacier’s Budget

Summer Rain

Year round Snow

Note that a glacier is a river. Even if the terminus doesn’t advance, still flows

Glacial FlowGlacial 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

Mechanics of Glacial FlowMechanics of Glacial Flow

Erosion by GlaciersErosion by Glaciers

• Abrasion– Rocks embedded in glacier’s base make

linear scratches and grooves in bedrock

• Quarrying– Glacier breaks off and removes large blocks

of rock. FROST WEDGING is important

Glacial Abrasion in BedrockGlacial Abrasion in Bedrock

Source: Tom Bean

Glacial Erosion – Roche MoutonéeGlacial Erosion – Roche Moutonée

Glacial Erosion – Roche MoutonéeGlacial Erosion – Roche Moutonée

Yosemite NP, Calif

Erosion by Glaciers (cont.)Erosion by Glaciers (cont.)• Alpine glaciers erode mountain slopes Alpine glaciers erode mountain slopes

into horseshoe shaped basins called into horseshoe shaped basins called cirquescirques– Melting forms cirque lake (Melting forms cirque lake (tarntarn))

• Erosion of two or more cirques erodes Erosion of two or more cirques erodes intervening rockintervening rock– Horns :pointy peaks made by triosHorns :pointy peaks made by trios

– Arêtes: long serrated ridges by pairsArêtes: long serrated ridges by pairs

– Cols: passes through the arêtesCols: passes through the arêtes

Alpine Glacial ErosionAlpine Glacial Erosion

Alpine Glacial ErosionAlpine Glacial Erosion

Origin of Hanging Valley

Yosemite FallsYosemite Falls

Valley GlaciersValley Glaciers

• Erode a large quantity of bedrock and sediment

• Convert V-shaped stream valleys into U-shaped glacial valleys.

U-ShapedU-Shaped Valley in Tracy Wilderness, Southeastern AlaskaValley in Tracy Wilderness, Southeastern Alaska

Seawater Flooded U-ShapedSeawater Flooded U-Shaped Valleys: FjordsValleys: FjordsBela Bela Fjord, BC

When glaciers melt, sea-level rises

Erosion by Continental GlaciationErosion 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

Erosion of Preglacial Lowlands (Finger Lakes)Erosion of Preglacial Lowlands (Finger Lakes)

Erosion of Lowlands (Great Lakes, Finger Lakes)Erosion of Lowlands (Great Lakes, Finger Lakes)

Source: U.S. Dept. of Interior, USGS Eros Date Center

Superior

Michigan

Huron

Erie

Ontario

Glacial Deposits - DriftGlacial 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 glacier’s channel and at its

terminus as a Moraine: – Terminal Moraine: hills of sediment left by a glacier’s

retreat.– Terminal Moraines may be reshaped by a later glacial

advance into Drumlins: rounded elongated hills perpendicular to their original orientation

Advance & Retreat: MorainesAdvance & Retreat: Moraines

Note moraine, retreat or stationary

Stationary Analogy:

Escalator

Stationary & Retreat: Moraine at TerminusStationary & Retreat: Moraine at Terminus

Large Granite Erratics Large Granite Erratics

Lateral and Medial MorainesLateral and Medial Moraines

Lateral and Medial Moraines Lateral and Medial Moraines – – Kennicott GlacierKennicott Glacier

Wrangell-St. Elias NP, SE AK

The Origin of DrumlinsThe Origin of Drumlins

Glacier retreats, leaving behinda terminal moraine. Later it

advances again, and reshapes the moraine into a drumlin.

Drumlins Drumlins Rochester,NYRochester,NY

Glacial Deposits - DriftGlacial 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

Origin of EskersOrigin of Eskers

Eskers in Coteau des Prairies, South DakotaEskers in Coteau des Prairies, South Dakota

Effects of GlaciationEffects 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

Formation of Terraces due to Crustal ReboundFormation of Terraces due to Crustal Rebound

Lowered Sea-level - LandbridgeLowered Sea-level - Landbridge

Glacier Distribution 20,000 yaGlacier Distribution 20,000 ya

Approximate Maximum

Lowered Sea-level exposed continental shelfLowered Sea-level exposed continental shelf

The Creation of Glacial Lake MissoulaThe Creation of Glacial Lake Missoula

Purcell Lobe blocks Clark Fork River

The Draining of Glacial Lake Missoula The Draining of Glacial Lake Missoula

Repeated many times, last time 13000 kya

Giant Ripples of the Missoula FloodingGiant Ripples of the Missoula Flooding

Causes of Ice AgesCauses 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

Milankovitch Cycles Milankovitch Cycles

100,000 years

Discussion: cool summers and wet wintersMoisture content of air masses

41,000 years

Cold Dry Winter Hot Summer

Warm Wet Winter Cool Summer

25,700 years

Discussion: Perihelion and Aphelion

One More Point On ThisOne 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

Earth’s Past Ice AgesEarth’s Past Ice Ages(oldest on bottom)(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

Permian Glaciation – Gondwana TillitesPermian Glaciation – Gondwana Tillites

Poorly SortedUnstratified

Cenozoic CoolingCenozoic Cooling

The Late Tertiary and Quaternary oxygen

isotope record measured in marine fossil shells

Evap. water and CO2 during glacial timeremoves 16O to glacier ice leaving 18O in oceans for CaCO3 shell

Pleistocene GlaciationPleistocene 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

Foraminifera tests - Ice AgeForaminifera tests - Ice Age

Evap. water and CO2 during glacial

removes 16O to glacier ice leaving 18O in oceans for CaCO3 shell

Also spiral direction & diversity dep T

Nebraskan

Kansan

Illinoian

Wisconsinan

> 30 pulses in 4 or so major groups

warm cold

Continuous Ice Sheet 20 kya then warmingContinuous Ice Sheet 20 kya then warming

Scoured 30 M below sea-level

Cold pulse from about 1300 to 1850 AD Cold pulse from about 1300 to 1850 AD (The so-called “Little Ice Age”)(The so-called “Little Ice Age”)

Climate has been warming since then.Climate has been warming since then.

Athabaska Glacier, Columbia Icefield, W. Canada

Discussion: Global Warming

Worldwide melting, Worldwide melting, regardless of cause, releases regardless of cause, releases CO2 and H2O and exposes CO2 and H2O and exposes dark land. The atmosphere dark land. The atmosphere receives and holds more heat, receives and holds more heat, and temperature rise.and temperature rise.

End of GlaciersEnd of Glaciers