Glaciers and Glaciation

Glaciers are the most effective agents of erosion, transportation, and deposits, but running water is the erosional agent most responsible for shaping the earth's surface.
 
 

Glacier - large long-lasting mass of ice formed on land & moves because of gravity.

Snow when compacted crystallizes to form glacier if there is wet accumulation
 
 

                        Accumulation, Compaction, Recrystallization
 
 

Two Types of glaciated terrains -
1) Alpine glaciers and
2) Continental
 
 

Theory of glacial ages - In times past, colder climates prevailed during which much more of the land surface of the earth was glaciated than at present.
 
 

Present Day Glaciers

 Distribution - Polar regions and temperate climates. Also, in warm climate zones but at high altitudes.~ 1/10 of land surface (1/3 during ice age) is covered by glaciers with 85% of this in the Antarctic and 10% in Greenland. Melting all of Antarctic glaciers will increase sea level by 60m (200ft).

 Types of glaciers - based on whether restricted by valley or not.

1) Valley glacier - prevalent in Alpine glaciers

2) Ice sheet - (50,5000 sq km) - associated with continental glaciers, only two ice sheets exist in the world - Greenland & Antarctic.

3) Ice cap - similar to ice sheet but smaller

4) Piedmont - broad lowland at base of steep mountains.
 
 
 
 

Formation and Growth of Glaciers
 

This is similar to the sequence of sediments and sedimentary rock and metamorphic. rock.

Transition between snow and glacier ice is called FIRN

Wasting or losing of glacier ice moving downwards under the influence of gravity
 
 

Iceberg - a break off ice that is floating freely.

Glacial budgets -
a) positive if gain is more than loss;
b) negative if loss is more than gain
c) balance is neither advancing nor receding
 

Glacial positive budgets - push outward and downward at their edges - called advancing glaciers.

                        Receding glaciers - for glacier with negative budget

                        Balanced budget - neither advancing nor receding
 
 

Zone of accumulation -

 Boundary between these - snow line

Zone of wastage
 
 

Snowline is a good indicator of the budget; if it migrates up, glacier shows sign of negative budget

Terminus - the lower edge of a glacier
 
 

Crevasses - open fissures that occur due to differential movement within the glacial ice

Icefall occurs when the glacier ice does not slow down when passing or descends a long, very steep slope
 
 

Movement of ice sheets - most movement is by plastic flow but some is due to sliding along its base

Movement of valley glacier

Two mechanisms-
1) Basal sliding

2) Plastic flow near the base 'bendable' nature of i.e itself
 
 

Glacial Erosion and features associated with it-

            1) Plucking and 2) Abrasion (abrasion leads to the creation of rock flow and glacial striations)

            Pebbles/graded sized boulders dragged along

Faceted - give a flat surface

Striations

Rock Flour - powder
 
    

Alpine Glaciation  features (click ont eh blue letters to see the drawings)
 
 

1. U-shaped valley (cross-profile) whereas V is characteristic of rivers

2. Truncated Spurs - lower part of ridges that have been (covered) into facets by glacial erosion

3. Hanging Valleys -

Rock-basin lakes - depression carved out of weaker rocks

4. Cirques - steep sided, rounded hollow carved into with mountain at the head of a glacial valley (help from weathering and erosion)

5. Horn - sharp peak that remains after cirques have cut back into a mountain on several sides

6. Arêtes - sharp ridges that separate glacially carved valley

7. Roche mountain is a small bedrock hill smoothed by the ice on the upper side and plucked to a rough face on the down side as the ice pulls frequently from points and cracks
 
 
 
 

Erosional Landscapes Associated with Continental Glaciation
 
 

1. Drift = all material of glacial origin

2. Till - unsorted and unlayered rock debris deposited by glaciers

3. Erratic - a boulder carried by ice usually not from the local bed rock. Tracing the source of the boulder could help indicated glacier direction.
 
 

Moraines - a body of till carried on or in a glacier, or left behind after glacial ice has receded.

1. Lateral moraines

2. Medial moraines occurs where glaciers meet

3. End moraines - Terminal moraine farthest along point of glacier, Recessional moraine

4. Ground moraines - fairly thin extensive layers of till

5. Drumlins - where ground moraine is reshaped into a stream-lined hill
  
6. Outwash - In wastage zone, large quantity of melt water material deposited by the debris - (lots of melt water) is called outwash.  This is silted and layered.

7. Esker - a long sinuous ridge of water-deposited sediment up to 10 meters high

8. Kettle - results when ice block left behind melts (depressional lakes)

9. Kames - small hills of sand and gravel dumped near edge of ice stratified draft
 
 

Glacier lakes and Varves

Glacier lake results from dam by glacial deposits

Varves...two layers in a glacier lake.... silt, clay represent one year's deposit...  this can be used to date a glacial lake
 
 

Effects of Past Glaciation

Last American glacial ice melted from Canada less than 10,000 years ago.

Older glaciers are difficult to date because of less evidence due to weathering/erosion occurring during warm interglacial periods & later ice sheets & valley glaciers overriding & obliterating many of the features of earlier glaciation.

Last glacial age was at its peak about 8,000 years ago

In N. America, thousands of lakes
 
 

Indirect effect

Pluvial lakes

Lowering of sea level

Fiord - a coastal inlet that is drawn glacially curved valley

Coastal rebound
 
 

Tillite - lithified till