Glacier: a Flowing Stream of Ice
Continental (Greenland, Antarctica)
Snowfall vs Melting & Evaporation (Ablation)
Zone of Accumulation
Snowfall Exceeds Melting & Evaporation
Excess Snow Turns to Ice & Flows Out
Zone of Melting or Ablation
Melting & Evaporation Exceeds Snowfall
Melting Excess Made up by Ice Flowing in
Terminus of Glacier
Snowfall & Inflow = Melting & Evaporation (Ablation)
Results of Glaciation
Mountain Glacier Landforms
Evolution of a typical mountain glacier landscape.
Continental Glacier Landforms
Two stages in the retreat of a typical continental glacier.
The Greenland Ice Cap shows the dome-like form of a typical continental glacier. Glacial Chronology
The table below gives an idea how complex the Pleistocene really was. Ice advances and retreats in different areas are given different names because it is not always certain that they began at the same time everywhere.
Time (1000 Years)
About 20 Glacial Advances
2000 (2 M.Y.)
Beginning of Pleistocene
4000 (4 M.Y.)
Dwarf forests still in Antarctica
First Glaciation in Antarctica
Pleistocene 3 M.y.
Permian 250-220 M.y.
Ordovician 450 M.y.
900-650 M.y. (Snowball Earth)
Earth seems to have alternated between "icehouse" and "greenhouse" episodes. The Greenhouse Effect
"A little greenhouse effect is a good thing" (Carl Sagan). Without a natural greenhouse effect, earth would be frozen. 90% of the earth's natural greenhouse effect is due to water vapor. Ever notice how hot nights are sticky? It's no accident - it's hot because it's sticky. High humidity results in a water-vapor greenhouse effect. In summer, both New Orleans and Phoenix might hit 100 F, but by midnight Phoenix could be down to 60, whereas New Orleans might still be 90. The difference is due to humidity and a water-vapor greenhouse effect. We can't do much about evaporation from the oceans, but we have been adding to the atmospheric load of carbon dioxide. Other important greenhouse gases are methane and oxides of nitrogen. Molecule for molecule, methane is twenty times more powerful than carbon dioxide as a greenhouse gas. Landfilling garbage (which releases methane) instead of burning it may not always be the best idea. Some scientists have proposed that abrupt warming episodes in earth's past may have been triggered by releases of methane. The Carbonate-Silicate Cycle
Earth has almost as much carbon dioxide as Venus
Volcanoes add carbon dioxide to the atmosphere
Carbon dioxide is removed from the air to make carbonate rocks Mountain-building favors cooling
Uplift exposes rocks to weathering
Calcium silicates (plagioclase, amphiboles, pyroxenes) are chemically weathered Calcium is carried to the sea where organisms bind it into carbonate minerals Creation of carbonates removes carbon dioxide from the atmosphere Weathering of carbonates returns carbon dioxide to the atmosphere Plate tectonics carries some carbonates into the earth
Heat liberates carbon dioxide
Carbon dioxide returns to the atmosphere
The cycle does not require life but does require liquid water. Uplift of the Himalayas resulted in delivery of huge volumes of...
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