16 - Glaciers as Landforms16 - Glaciers as Landforms• 2% of all water• 88% of FW• Covers

Antarctica and Greenland avg 2.5 km thick

• Max 4 km thick• During

Pleistocene 20% of water on land

AccumulationAccumulation and Ablation

Unconfined Ice Sheet

Geomorphology of Alpine GlaciersGeomorphology of Alpine Glaciers

• http://www2.wwnorton.com/college/geo/egeo/animations/ch18.htm

Equilibrium line ~snow line, maximum flow in x-sec. Glaciers much higher average surface gradient than streams

Valley Glaciers

A Cirque Glacier

End of Glacier Debris Flow

Importance of glaciersImportance of glaciers• Influence earth’s Influence earth’s

energy balance - energy balance - albedoalbedo

• Major component of Major component of (fresh) water storage (fresh) water storage – affects sea level– affects sea level

• Important agent of Important agent of landform evolutionlandform evolution

Center moves faster than margins. Note ogives, annual waves

ObstaclesObstacles• Upglacier, the movement

of ice closes joints in the rock. Only abrasion occurs.

• Downglacier, over the crest of the bedrock, ice flow opens joints. Meltwater gets into cracks and freezes, enlarging cracks. Plucking removes rock.

Davidson Glacier near Davidson Glacier near Haines, AlaskaHaines, AlaskaAn Alpine glacier systemAn Alpine glacier system

Ledges (obstacles) beneath ice reflected by Crevasse Fields and Ice Pinnacles (Seracs)

Accumulation zone extending, ablation zone and buried obstacle compressing

Terminus

Ice Caps and Ice Caps and Continental Ice SheetsContinental Ice Sheets

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

White, reflective, high latitude, positive feedback

Nunatak

Nunatak: exposed rocky area not covered with ice or snow

Byrd Glacier, Antarctica, an outlet glacierByrd Glacier, Antarctica, an outlet glacier

Zone of Accumulation

Outlet Glaciers

AblationAblation

AblationAblation

Vatnajokullhttp://pubs.usgs.gov/fs/2005/3056/

Formation of Glacier IceFormation of Glacier Ice

FirnBTW: note leading edges thrust over terminal debris

Ice DeformationIce Deformation

Accelerating

slowing

Wet GlaciersWet Glaciers• Warm = wet-based

• Cold = dry-based

• ρice < ρwater, therefore

Pressure increase on ice increases density to that of liquid water.

• Causes "melting point decrease“. Ice than would normally melt at 0oC = 32 o F now melts at a cooler temp. High pressure melting point called PMP - pressure melting point

– 0.7°C/ km of ice above you

• “Warm” ice = thick, fast

• Moves mostly by basal sliding on wet base

PressureMeltingPoint

Cold, High Polar, Dry BasedCold, High Polar, Dry BasedBase ice is frozen

These glaciers do not slide,

they only move by internal deformation

Plucking

Intermediate (subpolar)Intermediate (subpolar)

Temperate, Wet BedTemperate, Wet Bed

Striations, transport by subice flows

Rapidly Flowing GlaciersRapidly Flowing Glaciers

Observed Ice Core TempsObserved Ice Core Temps

• Greenland– Tbed < 0°C

• Antarctica– Tbed ≈ 0°C

Pressure Melting and RegelationPressure Melting and Regelation

• For ice near Pressure Melting Point:– Movement increases pressure, thus melting, on

the up-ice side of an obstruction– Movement away from the obstruction releases

pressure - causes freezing on the down-ice side – “regelation”

meltmeltmeltmelt

Effects of Pressure MeltingEffects of Pressure Melting

• High pressure is experienced on the up-ice side of an obstruction.

• Pressure melt results

• Water migrates around obstacle

• Regelation occurs in low pressure zone

MELTREFREEZE =REFREEZE ="Regelation""Regelation"

Erosion by PluckingErosion by Plucking• Melt then regelation

mix loose bed material and refreezing ice at base – gets into rock cracks, expands w/ freeze and pushes: “plucking”

AbrasionAbrasion

• Plucked material is available to wear away the bed – “abrasion”

Abrasion Features / chattermarksAbrasion Features / chattermarks

PolishPolish

• Typical of similar hardness (bed vs. tool) and fine load (~ sandpaper)

Glacial Abrasion in BedrockGlacial Abrasion in Bedrock

Source: Tom Bean

Glacier HydrologyGlacier Hydrology

Liquid water flows on, within,

and beneath glaciers

Subglacial ChannelsSubglacial Channels

• Eroded into bedrock

• Polar Glaciers– Pressure– Tools

Subglacial - Ice CavesSubglacial - Ice Caves

Ice CaveMendenhallGlacier, AK

Photographer:John Bortniak, 1991

NOAA Corps

Note Ice contact debris

To be continuedTo be continuedoutwash

terminus