Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Glacier: a Flowing Stream of Ice

Snowfall vs Melting & Evaporation (Ablation)

Lengthwise section of typical glacier

Zone of Accumulation

Zone of Melting or Ablation

Terminus of Glacier

Snowfall & Inflow = Melting & Evaporation (Ablation)

Results of Glaciation



Meltwater Erosion

Glacial Landforms

Mountain Glacier Landforms

Mountain Glacier Landscape

Evolution of a typical mountain glacier landscape.

Continental Glacier Landforms

Continental Glacier Landscape

Two stages in the retreat of a typical continental glacier.

GLICE1.GIF (9907 bytes) 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) Conditions North America
0-18 Interglacial
18-67 Glacial Wisconsin
67-128 Interglacial Sangamon
128-180 Glacial Illinoisan
180-230 Interglacial Yarmouth
230-300 Glacial Kansan
300-330 Interglacial Aftonian
330-470 Glacial "Nebraskan"
470-540 Interglacial  
540-550 Glacial  
550-585 Interglacial  
585-600 Glacial  
600-2000 About 20 Glacial Advances
2000 (2 M.Y.) Beginning of Pleistocene
4000 (4 M.Y.) Dwarf forests still in Antarctica
15 M.Y. First Glaciation in Antarctica

Ice Ages

The Greenhouse Effect

The Carbonate-Silicate Cycle

The Snowball Earth

Between 900 and 600 m.y. ago, Earth froze completely (or almost) about four times. Global freezing alternated with extremely rapid sea-level rise and global warming 


Possible reasons: 

Probable Sequence of Events

Milankovich Cycles

Cool Summers More Important Than Cold Winters

Axis Tilt

Shape of Orbit + Precession

Where We Stand Now

The earth's axial tilt reached a maximum about 9,000 years ago and was increasing for 20,000 years before that. The increasing tilt would have favored hotter summers, hence ice retreat. Just like sunlight reaches maximum in June, but summer is hottest in August, there's a time lag.

What Causes Ice Ages?

Within Earth (Endogenic)

Outside Earth (Exogenic)

Don't Really Know

Are We Headed For Another Ice Age?

Don't Really Know

Global warming due to fossil fuels may be catastrophic in many ways, but will probably not much affect these longer-term cycles. We will have run out of fossil fuels long before the duration of a typical interglacial.

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Created 20 January 1997; Last Update November 2, 1999
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