Glacial Deposition

1
Glacial Deposition

• Sub-ice deposits Till, Drumlins Erratics
• Ice-margin deposits Moraines

2
Characteristics

• Dominant process in ice sheets larger landforms
  than in valley glaciers
• A mix of sand, clay, boulders
• Unsorted (unlike sorted river deposits)
• Angular (unlike rounded river deposits)
• Contents/lithology help us to work out where ice
  came from
• Shape help us to determine direction of ice flow
• Deposits also called unstratified glacial drift

3
Sub-ice deposits

• Lodgement till
• Drumlins
• Erratics

4
Lodgement Till

• At the base of ice up to 50 of the volume may be
  debris
• Some deposited, mainly at the ablation zone
  (where melting gt accumulation), under the
  glacier. This is called till.
• Over time unsorted till layers build up angular
  fragments are set into sand silt
• This is lodgement till

5
DrumlinsA streamlined hillock, commonly
elongated parallel to the former ice flow
direction, composed of glacial debris, formed
under glacier (Hambrey 94)

• Ice laden with till is obstructed by irregular
  surface of lodgement till or bedrock
• Friction leads to deposition
• Cleaner ice in the layer
• above doesnt have enough
• energy to pick up till
• 4. But, enough drag to
• mould the till around the
• obstruction

6
Drumlin characteristics

• Often form near edge of glacier (the margin) so
  ice not especially thick
• Eg Drumlins of Southern Iceland ice 100-150m
  thick over drumlin field
• Formed at the ablation zone
• In UK formed during the last ice advance (called
  the Dimlington stadial) as they dominate edge of
  Lake District
• Longer drumlins form when ice travels fastest
• Size from 2m high 10m long to 50m high 5 km
  long
• Usually form in clusters, called fields or swarms

7
Drumlin in Wisconsin, USA
8
Partially submerged drumlin field (or swarm) in
Nunavut, Canada
9
Case studyVale of Eden, Cumbria, UK

• See handout
• Look at Figure 7.40
• Which way was the ice flowing?

10
Erratics

• Large boulders that have been transported by a
  glacier are deposited, often far away from their
  origin

• By comparing the lithology of the rock with
  possible sources the direction of ice flow can be
  worked out
• UK eg Granite boulders from Lake District lie
  on beach at Robin Hoods Bay, East Yorkshire

11
Ice-margin deposits

• Terminal moraines
• Recessional moraines
• Lateral moraines

12
Terminal (end) moraine

• Indicate the maximum ice advance.
• Crescent shaped
• May be a continous ridge or discontinous if
  destroyed by meltwater
• Larger glaciers produced larger moraines
• Eg the Cromer Ridge in north Norfolk (90m high,
  from the Dimlington ice advance)

13
Recessional (stage) moraine

• Similar to terminal moraine
• Marks a temporary halt in the retreat
• Eg Meridan glacier, Alaska, USA

14
Lateral moraine

• Lateral moraine forms along the edges of the
  glacier.
• Material from the valley walls is broken up by
  frost shattering and falls onto the ice surface.
• It is then carried along the sides of the
  glacier.
• When the ice melts it forms a ridge of material
  along the valley side.
• After the ice melts moraine
• Is altered by slope processes
• (eg slumping, solifluction)

Ngozumpa Glacier, Nepal