Picture of a glacier
The present areas covered by ice are about 10% of land surface
In past the maximum extent of ice was about 3 times the present spread and volume
If all ice were to melt - sea level would go up ~70 meters. If you only melt mountain glaciers and minor ice fields - sea level would go up 0.5 m
Glacial regime -
depends on balance between accumulation - mainly as snow,
and ablation by melting, evaporation, calving, wind erosion, avalanches.
Snow is transformed to ice
Snow = skeletal (hexagonal) ice crystals. As snow accumulates it traps air. The density of snow on the ground is.06-.08
- as the points of crystals melt it is transformed to granular snow. Density goes up to 0.2.
- firn = about 1 year old snow. Larger crystal size. - density 0.4-0.55.
- then gradually to ice by further recrystallization - density 1
Glacier flow
- Mechanism of flow - ice thickens until its center of gravity is high enough to cause ice to fall down hill. The movement is slow.
by - internal deformation or creep.
by basal sliding - helped by the presence of basal meltwater
Across a single ice stream the - maximum velocity is in the central portions.
In vertical profile - velocity decreases from surface to bedrock
Erosion by glaciers-
Attempts to quantify - measure silt discharged by glacier meltwater streams - get 1000-5000 m3/km2/yr
Compare with fluvial
Recognize glaciated areas by reorganized topographic features
Erosional
-local effects that consist of scratches, sculpted landforms
disrupted drainage
Drainage diversion
melt water erosion
Proglacial drainage
Depositional - glacial and fluvio-glacial
Deposits cover 1/3 of Europe, 1/4 N America 8% land surface of earth
Can tell glacial from fluvioglacial by grain size, sorting and stratification.
Glacial material called drift = all rock material transported in ice, deposits made by ice, and all deposits made by glacier melt water.
Characteristic sediments angular boulders and pebbles in matrix of sand and clay
glacial till
erratics
moraines - ridges of rock and earth debris
- ground
- lateral, medial
- terminal - Cape Cod and Nantucket
stratified drift - deposited by glacier meltwater
outwash - spread across land - Long Island
kames- isolated hills of sediment deposited in depressions or crevasses in ice
kame terrace - between valley glacier and valley side
Periglacial features (area next to border ice sheets)
To find out more about glaciers an excellent resource is: Glaciers and Glacial Geology, A hypertext for the appreciation of glaciers, and how they work, by the students in Geology 445 - Glacial Geology - Spring, 1999 Montana State University - Bozeman.