Glacial environments

Glacial environments

1. Glacial environments exist in arctic climates, restricted to the polar regions and high mountains.

   • There have been at least 3 ice ages when arctic climates were more extensive (Precambrian, Ordovician and Permo-Carboniferous).
     • We know this as the sediments produced are same as those now forming in the polar regions.
     • Ancient glacial deposits occur in places that are far from the modern poles, due to plate movement.

2. Products

   • Boulder clay
     • Formed when rock obscures movement of a glacier and the presseure of the ice on the upstream side of the rock causes local melting of the ice.
       • The water flows to the downstream side of the rock where it freezes in any fractures that exist in the rock.
         • This allows the ice to pluck large fragments away as it refreezes and the ice moves on due to gravity.
     • Fragments of rock at the base of a glacier scratch striations on underlying rock surfaces.
       • Abrasion during transport produces fine grained, crushed rock fragments.

3. Processes

4. Examiner tips

   • How ancient glacial deposits are recognised.
     • Striations- The scratches formed by rocks carried in moving ice.
       • Can be used to tell the direction of movement of ancient ice ages.
     • Tillite- The rock formed from very poorly sorted and varied material dropped by the ice.
     • Varves- the annual lake clays and silts in distinctive thin layers.
     • Fluvio-glacial sands and gravels.

5. Westray

   • North-west Orkney
   • Evidence of ice advance in the late Devensian around 30,000 years ago.

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