GLACIERS
AND
THEIR
EFFECTS
GLACIER
A body of ice
Formed on land
Recrystallization of snow
Evidence of movement
Theory of glacial ages
– at present ~10% of land surface glaciated
– in past, ~32% of land surface glaciated
GLACIOLOGY
Distribution of present glaciers
– Alpine vs. Continental glaciers
– Develop where all of annual snow doesn’t melt away in warm seasons
» Various climates
– Most glacial ice in Antarctica
– Glaciers in US
Types of Glaciers
– Valley glaciers- “ice streams”
» Move down valley
– Ice Sheets & Ice Caps
» Flow from high part outward
Antarctic slide show
Growth of glaciers
– Snow => Firn => Glacier Ice
Wastage (ablation) of glaciers (“shrinkage”)
– Melting
» more melting at lower elevations
– Evaporation
– Calving into Icebergs
» where a glacier flows onto a sea
GLACIER BUDGET
Positive--Advancing Glacier
– Terminus moves forward
Negative--Receding Glacier
– Terminus retreats
Zone of accumulation
– Where some snow remains after the melt season
Zone of Wastage
– Where all snow & some glacier melt
Snow line
– Boundary between two zones
Movement of Valley Glaciers
Gravity driving force
Faster above & in middle of glacier
Basal sliding
Plastic flow
– “flowage”
Internal flowage (plastic flow)
Rigid zone
– Crevasses may form here
EROSION BY GLACIERS
Under glacier
– Polishing and rounding
» “Sheep Rocks”
– Striations- scratches & grooves on rock
– Rock flour produced & washed out of glacier
Above glacier
– Frost wedging takes place
– Erosion by glaciers steepen slopes
– Angular & rugged landscapes created
Alpine landscapes due to erosion
– U-shaped valleys
– Hanging valleys
– Truncated spurs
– Cirques- at heads of valley glaciers
– Rock steps
» Rock basin lakes
– Horns (saw tooth mountains)
– Aretes
– Landscapes due to continental glaciation
DEPOSITION BY GLACIERS
Till
– Unsorted debris
Erratic
Moraine- body of till
– Lateral Moraine
– Medial Moraine- where tributary joins glacier
– End moraine» Terminal
» Recessional
– Ground moraine
» Drumlins
Outwash
– Stream-deposited sediment
» sorted
– Braided streams typical
– Kettles
Glacial Lakes
– (Varves)
Effects of Glacial Ages
4 major advances during past 2 million years (Pleistocene)
– Latest peaked 20,000 years ago
– Ended 10,000 years ago
Direct effects
– Scoured much of Canada & New England
– Cut Great Lakes
– Flattened Midwest
– Extent of ice in N. America
– Sierra & other mountains had larger valley glaciers
Indirect effects
– Lowered sea level 400 feet
– Wetter climate
– Pluvial Lakes
» Some were large lakes in west
Lake Bonneville
Death Valley a lake
– Crustal rebound
Older Glacial Ages
Late Paleozoic
Late Precambrian