Glaciers and ErosionChapter 7 Section 1

Glaciers - Natural Forces compact snow to create an enormous mass of moving ice.

GLACIERS ARE POWERFUL AGENTS OF EROSION!

Forming GlaciersGlaciers form at

High Elevations or Polar Regions where the snow remains all year

http://www.youtube.com/watch?v=MQhtlddskDs

Snowfield or IcefieldAn almost

motionless mass of permanent snow and ice formed by accumulation above the snowline.

Covers most land near poles and some mountain tops.

Required ConditionsAvg. temperatures

remain at or near freezingThis causes partial

melting and refreezing changing the snow into grainy ice crystals called firn.

Snow accumulates squeezing air out and flattening it.

After the firn is flattened and the air squeezed out, it becomes a steel-blue color

Is it a glacier yet?A Glacier is not

formed until the snow and ice is thick enough to move due to GRAVITY.

Glacial formation is greatest in regions where temperatures are LOW and snowfall is HIGH

How Does a Glacier Grow?Growth depends on

how much snow is received and how much ice is lost(evaporation and melt).

Increase – New snow is added faster than it melts, evaporates, or breaks off into the sea as an ICEBERG

Decrease – Ice disappears faster than the snowfalls

Types of GlaciersValley Glacier in the Swiss Alps

Valley GlacierLong, narrow,

wedge-shaped masses of ice

Found in high mountain regions Alps Himalayas Andes Alaska New Zealand

Continental Ice SheetOccupies millions of

square kilometersGreenland

90% buried 3000m at its thickest

Antarctica Largest in the World Some areas up to

4000m thick! Worldwide sea-levels

would rise by more than 60 meters if they both melted.

http://www.foxnews.com/story/0,2933,554123,00.html

Glacier Movement ~100m per yearBasal Slip

Water on the bottom of glacier acts a lubricant between the ground/rock and ice because the pressure causes it to melt.

Movement continuedCalvingInternal Plastic Flow

Solid ice crystals slip over each other causing a slow forward motion

Rate affected by Slope Thickness And Temperature

Faster at surface than bottom

Friction

Glacial FeaturesCrevasses – large

cracks in the surfaceCan be greater than

30m deepCan be covered by

snow

Ice ShelvesIce sheet that has

moved out over the oceanRoss Ice Shelf,

AntarcticaIcebergs – large

blocks of ice that break off and drift in the ocean

Largest ice calving on camerahttp://www.youtube.

com/embed/hC3VTgIPoGU?rel=0

Landforms Created by GlaciersCirque – bowl

shaped depression

arêteSpiney, sharp,

jagged ridges between cirques.

HornAretes join together

forming sharp, pyramid peakes

Roches moutonnees (sheep rocks)Solid rock can be

polished, scraped, and scratched by glaciers. Large projectiles are rounded

Side facing glacier is smooth

Side opposite is steep and jagged from rock being pulled away by ice

U-Shaped ValleysCan only be created

by glacial erosion – glaciated valley(v-shaped valleys

are from running water)

Hanging ValleySmall tributary

glaciers flow into main valley glaciers

Smaller tributary glacial valleys are left above main valley floor

Glacial DepositionMaterial (rocks and

dirt) are trapped in glacial ice.

When the glacial ice melts – the rocks and dirt are deposited

Types of Glacial Deposit Materials

Erratics – large bouldersGlacial drift – gen. term

for all sediments deposited by glaciers.

Till – unsorted sediment that has been scraped off by base of glacier

Stratified drift – sorted material that is deposited by streams flowing from melting glacial ice (melt water)

Till DepositsMoraine – landform

made by glacier till deposits.Lateral Moraine –

side of valley/long ridge

Medial Moraine – 2 valley glaciers meet and their lateral moraines meet creating a dark strip of deposits

Till Deposits continuedGround Moraine – unsorted

material left behind when a glacier melts. Landscape of Ohio,

Montana, and Canada

Drumlins – tear shaped mounds of till usually found in clusters parallel to the direction of glacier movement.Bunker Hill Revolutionary

War Battle actually took place in neighboring drumlin called Breed’s Hill

Ice AgesMilankovitch Theory – small regular changes

in the earth’s orbit and tilt of the earth’s axis causes ice ages

41,00o years the earth’s tilt goes between 21.5 degrees and 24.5 degrees