Glaciers: Glaciers: thethe Work of Ice Work of Ice

Stephen J. Krasemann/DRK Photo

Glacier

• Body of ice, snow, firn, and meltwater lying wholly or mostly on land showing evidence of present or former movement

• Glaciers form where more snow accumulates in winter than melts in summer - above snowline

Variations in the Variations in the Present Height of Present Height of

the Snow Linethe Snow Line

Types of Glaciers

alpinealpine: restricted to mountainous systems

continentalcontinental: covers extremely large areas - ice caps, ice sheets

AntarcticaAntarctica: 12,500,000 km2 up to 3 km thick, 80% of the ice on earth, 65% of the fresh water

Greenland:Greenland: 1,700,000 km2 3.2 km thick

Common types of alpine

glaciers

Valley Glaciers, Denali National Park

Greenland Greenland Ice CapIce Cap

Betty Crowell

Sentinel Range, Antarctica

Glacial growth: Accumulation

Transformation of snow into iceTransformation of snow into ice

SnowSnow may be thought of as sediment,

FirnFirn as sedimentary rock, and

Glacier iceGlacier ice as metamorphic rock.

Transformation Transformation of Snow to of Snow to Glacial IceGlacial Ice

Z. Xie/Lanzhou Institute of Glaciology, Academia Sinica, People’s Republic of China

Polarized

Thin Section of Ice

Glacial BudgetGlacial Budget

Glacial shrinkage: Ablation

• Melting

• Iceberg calving

• Sublimination

• Wind erosion

Tom Bean

Calving Glacier,Glacier

Bay,Alaska

Iceberg near AntarcticaIceberg near Antarctica

Mechanisms of motion in glaciers

• Type of motion depends on depth.

• Upper 50–100 m: brittle

• > 100 m: plastic (layers of ice slide past

each other)

• Individual slips extremely small

• Motion at base can be by slip or lubricated by water.

Cold, Dry GlacierCold, Dry Glacier

Wet GlacierWet Glacier

Rates of motion

• Extremely variable from one glacier to another

• Millimeters to meters per dayMillimeters to meters per day

• Some glaciers move in surges: periods of rapid movement following periods of quiescence.

• During surge, rates may be 50 m/day.During surge, rates may be 50 m/day.

• Rates vary with position in the glacier & season of the year.

Glacial Glacial flow and flow and

basal basal slidingsliding

Ice Flow in Ice Flow in Typical Typical

Temperate Temperate Valley Valley GlacierGlacier

John Turner/Tony Stone Images

Glacial Crevasses, New Zealand

Ice Flow in a Continental GlacierIce Flow in a Continental Glacier

Wolfgang Bayer/Bruce Coleman

Beardmore Glacier, AntarcticaBeardmore Glacier, Antarctica

Fast flow lines

Stages of Stages of Antarctic Ice Shelf Antarctic Ice Shelf

RetreatRetreat

Glacial erosion

AbrasionAbrasion - ice is soft, tools do the job - striations, polish, friction cracks

Quarrying (plucking)Quarrying (plucking)

U-shaped valleys & hanging valleys

cirques, horns, artet, rock flour

Glacial Polish, Striations,

and Grooves, Glacier Bay

National Park,Alaska

Carr Clifton

Glacial Glacial grooves and grooves and

striations striations at the base of at the base of

the Matterhornthe Matterhorn

S. C. Porter

Roche Moutonée

Asymmetrical glacial sculpturingAsymmetrical glacial sculpturing

S. C. Porter

Direction of ice flowDirection of ice flow

S. C. Porter

Carlyn Iverson/Photo Researchers

Glacial Cirque, AlaskaGlacial Cirque, Alaska

U-shaped Glacial Valley,

Glacier National Park,

Montana

Steve Kaufman/DRK

U-shaped U-shaped valleys and valleys and

fjords in fjords in northeasternortheastern Canadan Canada

S. C. Porter

Peter Kresan

McCarthy Fjord, Kenai Fjords National Park, Alaska

Creation of Creation of Hanging Hanging

Valleys and Valleys and Associated Associated Waterfalls, Waterfalls, Before and Before and

After After GlaciationGlaciation

Glacial deposits

1. ErraticsErratics2. Glacial driftGlacial drift

Unsorted SortedTILL

outwashkame eskers

loess/varves3. MorainsMorains: ridges of tillEnd, Lateral & Medial

S. C. Porter

Glacial erratic

Glacial Till on the

Eastern Side of the Sierra

Nevada

Martin Miller

S. C. Porter

Glacial tillGlacial till

Varves Formed in Glacial Lake

John S. Shelton

Glacial DepositsGlacial Deposits

Stephen J. Krasemann/DRK Photo

LateralMoraines

MedialMoraines

Courtesy USGS

Surging tributary glacierSurging tributary glacier

Terminal moraineTerminal moraine

Courtesy Gerald Osborn

Melting Ice

ResultingFeatures

Tom Bean/DRK

Drumlins in Wisconsin

Tim Hauf Photography/Visuals Unlimited

Esker in CanadaEsker in Canada

E.R. Degginger

Kames and Kettles in New Zealand

Kettle

Kame

John S. Shelton

Typical “Hummocky” Terrain Typical “Hummocky” Terrain of Glacial Tillof Glacial Till

Distribution of Distribution of Permafrost in Permafrost in the Northern the Northern HemisphereHemisphere

Lateral variations in permafrost in Siberia

GLACIATIONSGLACIATIONS

• Several periods in past• Worldwide & essentially

instantaneous (10 years)• Continental glaciers advance

and retreat several times•

Pleistocene continental glaciation

Great ice sheets extended into temperate regions 4 times in the past 2 million years:

Wisconsin 0.20 – 0.018 Ma

Illinoian 0.55 – 0.40 Ma

Kansan 1.40 – 0.95 Ma

Nebraskan 2.00 – 1.75 Ma

Isotopic record Isotopic record of changing of changing ice volume ice volume

over the past over the past 2 million years 2 million years

based onbased on deep-sea cores deep-sea cores

Fig. 12.32

Changes in Oxygen Isotope Ratios in Changes in Oxygen Isotope Ratios in Marine FossilsMarine Fossils

Sea level changes

Lots of water in glaciers - during last ice age sea level lowered by ~130 m130 m

* shoreline 100 km from NYC - Bering Strait, English Channel, Indonesia

(If all ice in glaciers today melted, sea level would rise 65m65m - Florida, Egypt, Hong Kong, London, Houston would be gone)

Glaciation in the geologic record

1. Ancient glacial deposits (till, dropstones, striations) indicate other periods of significant glaciation.

2. Late PC (Snowball Earth), Ordovician, Permian

Glaciation in Glaciation in North North

AmericaAmerica

What causes ice ages?

• Variations in Earth's orbitVariations in Earth's orbit

• Changes in the atmosphereChanges in the atmosphere

• Changing position of the continentsChanging position of the continents

• Changes in circulation of sea waterChanges in circulation of sea water

• Sliding of Antarctic ice sheetSliding of Antarctic ice sheet

No single one of these explains all ice

ages – must be some combination.

Ice cores from the Vostok

Station, Antarctica

R.J. Delmas, Laboratorie de glaciologie et geophysique de l’environnement, Centre National de la Recherche Scientifique

After J.W.C. White (1993)

Copyright N.W. Driscoll, Woods Hole Oceanographic Institute

Thermohaline Oceanic Circulation

Retreating Rhone GlacierRetreating Rhone Glacier

S. C. Porter