glaciers

“ RIVERS OF ICE ” Mass movement of frozen ice on land Mass movement of frozen ice on land Form at high elevations or high altitude Form at high elevations or high altitude Last extension of ice here began 20,000 years ago and receded about 10,000 years ago. Last extension of ice here began 20,000 years ago and receded about 10,000 years ago. Today only covers 10% of land surface Today only covers 10% of land surface

Ice Flow Glaciers are not static they are dynamic Glaciers are not static they are dynamicFormation: A steady accumulation of snow piles up and compresses layers beneath – these compressed layers turn into ice A steady accumulation of snow piles up and compresses layers beneath – these compressed layers turn into ice Force of gravity continuously pulls ice downward Force of gravity continuously pulls ice downwardMovement: Fastest ice is found on the surface at center of valley Fastest ice is found on the surface at center of valley Rate varies from a few cm to meters per day. Rate varies from a few cm to meters per day.

There are 3 Categories of Glaciers 1. Valley (Alpine) Glaciers found in mountainous regions found in mountainous regions high altitudes high altitudes Ex. Alps (New Zealand and Europe), Rockies Ex. Alps (New Zealand and Europe), Rockies

Valley or Alpine Glacier

Ice Sheets (Continental Glaciers) Much larger Much larger Flow direction is from an area of thick ice to thin ice Flow direction is from an area of thick ice to thin ice Ex. Greenland, Antarctica Ex. Greenland, Antarctica

3. Tidewater Glacier Flow far enough to reach out into the ocean Flow far enough to reach out into the ocean Create icebergs Create icebergs

Snow calving

Glacial Retreat

Budget of a Glacier Glacier accummulation = snow adds to the weight of a glacier Glacier accummulation = snow adds to the weight of a glacier Glacier Wastage (ablation) = melting and calving. Glacier Wastage (ablation) = melting and calving. When accummulation is greater than wastage = glacier advances When accummulation is greater than wastage = glacier advances When accummulation is less than wastage = glacier retreats When accummulation is less than wastage = glacier retreats If accummulation = Wastage = glacier remains stationary If accummulation = Wastage = glacier remains stationary

Glacial Erosion – Two Key Methods Plucking and Abrasion Features of Glacial Erosion: Features of Glacial Erosion: U-shaped valleys, sharp ridges (Aretes), pyramid peaks (Horns), water-filled valleys (Fjiords), and bowl shaped valleys (Cirques. 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 Glaciers aka Glacial Dump Drift = any sediment deposited by moving ice Drift = any sediment deposited by moving ice 2 Types: 1. Stratified Drift = well-sorted sediments deposited by streams (meltwater) 2. Till = unsorted sediment, deposited by moving ice

Deposits of Till  ｷ lateral moraines form along valley walls  ｷ medial moraines form where 2 lateral moraines meet  ｷ end moraine left at terminus of glacier where it retreats

Drumlins A drumlin is tear-shaped ridge showing direction of ice flow A drumlin is tear-shaped ridge showing direction of ice flow

Drumlins

Glacial Erratics Compositon of the deposit is different from the bedrock below Compositon of the deposit is different from the bedrock below

Deposits of Stratified Drift Kame :a small hill forms where sediments accumulate beneath ice. Esker: forms from under-glacial streams Kettle: a depression that can be water- filled Kame :a small hill forms where sediments accumulate beneath ice. Esker: forms from under-glacial streams Kettle: a depression that can be water- filled

Kames

Eskers One of many eskers running across the northwest of Canada One of many eskers running across the northwest of Canada

Muir Glacier 1941 and 2004

Massive melting – Holgate glacier, Alaska 1909 and 2004