“rivers of ice” mass movement of frozen ice on land form at high latitude or high elevation last...

Glaciers

“RIVERS OF ICE”Mass movement of frozen ice on landForm at high latitude or high elevationLast extension of ice here began 20,000 years

ago and receded about 10,000 years ago.Today only covers 10% of land surface

Ice Flow

Glaciers are not static they are dynamicFormation:A steady accumulation of snow piles up

and compresses layers beneath – these compressed layers turn into ice

Force of gravity continuously pulls ice downward

Movement:Fastest ice is found on the surface at

center of valleyRate varies from a few cm to meters per

day.

There are 3 Categories of Glaciers1. Valley (Alpine)

Glaciersfound in

mountainous regions

high altitudesEx. Alps (New

Zealand and Europe), Rockies

Valley or Alpine Glacier

Ice Sheets (Continental Glaciers)Much largerFlow direction is

from an area of thick ice to thin ice

Ex. Greenland, Antarctica

3. Tidewater GlacierFlow far

enough to reach out into the ocean

Create icebergs

Ice calving

Glacial Retreat

Budget of a GlacierGlacier accummulation = snow adds to

the weight of a glacierGlacier Wastage (ablation) = melting and

calving.When accummulation is greater than

wastage = glacier advancesWhen accummulation is less than wastage

= glacier retreatsIf accummulation = Wastage = glacier

remains stationary

Glacial Erosion – Two Key MethodsPlucking and Abrasion

Features of Glacial Erosion:U-shaped valleys, sharp ridges (Aretes),

pyramid peaks (Horns), water-filled valleys (Fjiords), and bowl shaped valleys (Cirques).

Glacial Erosion

Striations and Grooves

Depositional Features of Glaciersaka Glacial Dump Drift = any sediment deposited by moving

ice2 Types:1. Stratified Drift = well-sorted sediments

deposited by streams (meltwater)2. Till = unsorted sediment, deposited by

moving ice

Deposits of Till

lateral moraines form along valley walls

medial moraines form where 2 lateral moraines meet

end moraine left at terminus of glacier where it retreats

DrumlinsA drumlin is

tear-shaped ridge showing direction of ice flow

Drumlins

Glacial ErraticsLarge boulder left behind by the glacier

Deposits of Stratified DriftKame : a small hill

forms where sediments accumulate beneath ice.Esker: forms from under-glacial streamsKettle: a depression that can be water-filled

Kames

EskersOne of many

eskers running across the northwest of Canada

Muir Glacier 1941 and 2004

Massive melting – Holgate glacier, Alaska 1909 and 2004