Glaciers

Glaciers

1. flowing ice

   • begins to flow when thickness is 30-40 m
     • plastic flow
       • advance
         • rate of accumulation exceeds rate of ablation
           • ice front moves forward
       • retreat
         • rate of ablation exceeds rate of accumulation
           • front retreating; ice front melts
       • stationary
         • rate of accumulation = rate of ablation
           • ice front stays in same place
     • top of glacier moves faster than bottom

2. form by accumulation and metamorphism of snow

   • when rate of snow accumulation greater than rate of evaporation
     • zone of accumulation
     • zone of ablation
       • rate of melting and evaporation exceeds rate of accumulation

3. Valley Glaciers

   • form in mountains, flow down valleys
     • U shaped valleys
       • hanging valley
       • horns
       • arrêtes
       • truncated spurs

4. Continental Glaciers

   • form on land near north and south poles
     • moraines- deposits of till
     • outwash deposits= sand, gravel
     • kettle lakes= ice block in moraine leaves an impression= becomes lake
     • drumlins= hills moulded from till
     • eskers= ridge of deposits from rivers underneath glacier
   • very extensive and thick

5. erode, transport and deposit sediments

   • erosion
     • pick up or quarry out rock/sed.
     • sed. added from mass wasting
   • transportation
     • in suspension in the ice
     • on top
     • pushed in front like a bulldozer
   • deposition
     • till--- moraines
     • erratics
     • glacial outwash formed by re-worked till
     • blown by wind--- sand dunes and loess deposits
     • varves= seasonal landforms when sed. deposited in lakes

6. Pleistocene: Ice Age begins

   • several glacial periods occurred
     • cyclical
       • causes
         • continents located in polar region
         • adequate precipitation
         • relativ. low global temp.
           • decreased temp. related to mountain building
             • uplifted continents requires more weathering= takes CO2 from atmosphere
               • decreases GHG effect= cools earth
           • ~ 5 degrees colder than now
     • continental glaciation= few times in earth history
   • effects of most recent ice age
     • erosion and depostion
     • sea level changes
     • more rain during glaciations
     • v. windy along front of glacier: forms sand dunes and loess
     • drainage pattern change
       • deranged draining
     • depression of land
       • isostatic rebound
     • migrations and extinctions

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