glaciers RIVERS OF ICE Mass movement of frozen

glaciers

“RIVERS OF ICE” • Mass movement of frozen ice on land • Form at high elevations or high altitude • Last 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 dynamic Formation: • 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 valley • Rate varies from a few cm to meters per day.

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

Valley or Alpine Glacier

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

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

Snow calving

Glacial Retreat

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

Glacial Erosion – Two Key Methods Plucking 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 Glaciers aka Glacial Dump • 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 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 • ｷ

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

Drumlins

Glacial Erratics • 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 waterfilled

Kames

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

Muir Glacier 1941 and 2004

Massive melting – Holgate glacier, Alaska 1909 and 2004