Glacial Movement cont' Variations with Time 3

1
Glacial Movement (cont.)Variations with Time - 3

• Hydraulic lifting
• Water buildup along base. Pore pressure
  increases. Friction reduced until threshold
  crossed. Surge takes place.

2
Mass Balance of Glaciers (cont.)Definitions

• Zone of accumulation where accumulation gt
  ablation
• Zone of ablation (wastage) where ablation gt
  accumulation
• Equilibrium line line where accumulation
  ablation in a given budget year. Approximated by
  firn line firn limit snowline
• Budget year time of maximum ablation one year
  to the next will not usually be 365 days.

3
Mass Balance of Glaciers (cont.)Field Relations

• Snowline on Conway Glacier Canadian Rockies near
  Banff

4
Mass Balance of Glaciers (cont.) Definitions - 2

• Net mass balance difference between
  accumulation and ablation for whole glacier
  over budget year. Other names economy,
  budget, regimen

5
Mass Balance of Glaciers (cont.)Diagrams of
Relationships
Zone of Accumulation
Equilibrium Line
Zone of Ablation
6
Mass Balance of Glaciers (cont.)Diagrams of
Relationships
Zone of accumulation
Zone of ablation
Equilibrium line
Zone of Erosion
End moraine
Zone of Transportation
Zone of Deposition
7
Mass Balance of Glaciers (cont.)Diagrams of
Relationships
Equilibrium line
Equilibrium line
Icebergs
8
Mass Balance of Glaciers (cont.)Diagrams of
Relationships
9
Mass Balance of Glaciers (cont.)Methods of
Nourishment and Wastage
10
Mass Balance of Glaciers (cont.)Wasting (cont.)

• Downwasting, or thinning, is usually more
  important than recession.

May Stagnate
11
Mass Balance of Glaciers (cont.)Relationship to
Movement

• Large accumulation means high flow rates, even if
  the glacier is in equilibrium. Fig.
  4.8Results in more erosion, transportation.Favor
  able conditions 1) temperate conditions 2)
  maritime climatesPosition of terminus related to
  mass balance 1) positive advance 2) negative
  recession 3) equilibrium stationary (favors
  forming end moraine)

12
Ice Structures

• StratificationWinter ice thicker,
  finer-grained, debris-free.Summer ice
  thinner, coarser, debris-rich.May be deformed
  as the glacier moves. Figure 9.21/315

13
Ice Structures

• FoliationProduced by shearing Figure 9.22/316

14
Ice Structures (cont.)

• Crevasses
• Develop perpendicular to direction of maximum
  elongation.
• Types
• 1) Splay (radial) near centerline where
  spreading occurs. 9.23/317
• 2) Chevron near margin due to friction with
  valley walls.
• 3) Transverse extending flow, principally in
  ice falls. 9.24/318

15
Ice Structures (cont.)

• Ogives
• Annual bands produced as ice goes over ice
  falls. 9.3/300
• Winter ice clear crevasses covered.
• Summer ice debris-rich washed into open
  crevasses, which close below ice falls. 9.25/318
• Do not extend to much depth.

16
Morphologic Classification of Glaciers

• Niche, cliff, or slab glaciers above valley heads
  or sides
• Cirque glacier
• Valley or alpine glacier
• Outlet glacier tongues from ice caps
• Piedmont glacier T9.2/299 at foot of mountain
  range
• Mountain ice cap
• Ice cap
• Continental ice sheet