Glaciers - The Work of Ice
Glaciers



2% of the Earth's water is contained in glaciers. Of the nearly 
15,000,000 square km of ice covered regions, about 14,500,000 
square km are in Antarctica(12,600,000) and Greenland 
(1,800,000).


Formation of Glaciers


Requires a setting in which snow remains on the ground year 
round - SNOW LINE   elevation above which snow remains 
year round

Fresh snow is very porous - pore spaces are filled with air


With increasing time and pressure snow flakes recrystallize 
and the porosity is reduced - firn


After several years the lower part of the snow bank has been 
converted to firn
With increasing time the porosity of the ice is reduced to ~0% - 
glacial ice
When the ice reaches ~20 meters it begins to flow (plastic 
behavior) aided by gravity
The upper portion flows more rapidly than the base (due to friction 
and freezing at the base)
The upper portion may behave as a brittle substance and fractures 
(crevasses) are common







Near the "head" of the glacier is the zone of accumulation
Near the "foot" of the glacier is the zone of ablation 
(processes leading to melting)
If accumulation is greater than ablation then the glacier 
advances
If ablation is greater than accumulation then the glacier 
retreats
Glaciers transport large volumes of rock material (poorly 
sorted) in front, on top and at the base of the ice.


Glacier Types



Ice Sheets - Antarctica and Greenland : some is more than 
4000 meters thick
Ice Shelves - ice sheets that extend over marine waters
Ice Caps - small ice sheets
Valley Glaciers
Piedmont Glaciers



Glacial Erosion



Striated (groved) bedrock
Glacial Polish
Glacial Valleys - "U"-shaped
Cirques - bowl-shaped areas
Arette - glacial ridges - intersection of two cirques
Horns - spires left behind - intersection of several cirques





Depositional Features


Till - unconsolidated glacial debria - poorly sorted
Moraines - terminal, lateral and medial depending on where 
the material was transported.
erratics - diamonds in Ohio
Kames - 
    Kettel Lakes


Causes of Glaciation


Plate Tectonics - lithosphere transported to a polar region
Changes in temperature - prevent or encourage accumulation
Variations in properties of the Earth's orbit.