Where and how do glaciers form

      Form in mountains or on continents

      Created by accumulation of snow

            12” of snow =~1” rain

                  Density of H2O + 1g/cm3

                  Ice has a lower density than water due to structure

Neve (density = 0.16-0.4 g/cm3)

Firn (density =0.4-0.8 g/cm3)

                  Glacial Ice (density = ~0.9 g/cm3)

      To create Glacial Ice you must have a great deal of pressure

            Generally this equals about 100-180 ft of snow accumulation

Progression:

Snowà Neveà Firnà Snowfield or Firnfiel

                                            Glacial ice (more 

than 100 ft of snow 

pack)                                             

All Glaciers Flow

Wet Bottom Glaciers

      Water along base of glacier

      Melting occurs due to heat from ground

      Slides along base

      Surges occur when water builds up

Dry Bottom Glaciers

      Colder regions

      Base of glacier adheres to bedrock

      Flows internally

Internal Flow

      Plastic Deformation

      All glaciers flow plastically

      Occurs below ~60 meters in depth

      Above this region brittle deformation

            Crevasses form

Average Rate of Motion

      100-300 m/year depending on conditions

      Top center of glacier moves the fastest

Glacier movement can cause scouring of rock surface they flow over

      Plucking (Roche Moutonnes form)

      Striations

The amount of accumulation compared to the amount of metling is the budget of a glacier

Glacial Zones

      Zone of ablation:  region were melting is occurring

      Zone of accumulation:   region where snowfall accumulates

            Above the firn line

      Terminus or Toe is the leading edge of the glacier

Glacial Features created by depostion

      Moraines:  Rock debris dropped out by a glacier

            Lateral moraines

            Terminal moraines

            Medial moraines

      Kettle lakes

            Lakes created as large piece of glacial ice melts

      Calving

            Large pieces of ice breaking off of glacier to create icebergs

      Outwash plains and Kame terraces

            Outwash plains are regions of sediment deposited by glacial run off

            Kames terraces are terraces left alongside a glacier by glacial run off

      Eskers and Drumlins

            Eskers are under glacial rivers that leave a gravel/till channel

            Drumlins:  enlongated hill like structures created as sediment drops out of a glacier

Erratics and Loess

Erratics: Rocks dropped out from a glacier

            Loess:  Glacial rock flour carried by wind and deposited

Glacial features created by carving

      Horns and Aretes

      Cirques and Tarns

U-shaped Valleys

Last period of Global Glaciation

Effects of this glaciation

      Continental shelves:

cut down 300’ below present

      Drowned stream valleys

      Lakes of Glacial origin

      Lakes that Occupy valleys cut by glaciers

Lake Chelane

Lake Okanogan

      Lakes formed by Moraines

Santiam Lake

Wallowa Lake

Isostatic depression and rebound

Great lakes regin

            North East N. America

Puget sound

      Catastrophic Floods and Pluvial lakes

Lake Bonneville

Lake Malheur

Catlow Lake

Lake Lahontan

What Causes Glacial Cycles

Milankovitch cycles

Other contributing factors

      Change CO2 levels:

      Decaying plants

      Volcanic activity

      Coral Reefs

Albedo

            Ice has high albedo (reflect energy)

            Lots of ice…cold climate

                  Lots of rock absorbs heat back and warms atmosphere

Current Status:

Greenland Ice sheets

Changing ocean circulation