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.

Greenland Ice Cap 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 Alps Northern Europe Poland-Russia
0-18 Interglacial
18-67 Glacial Wisconsin Wurm Vistula Varsovian
67-128 Interglacial Sangamon Uznach Eem Masovian
128-180 Glacial Illinoisan Riss Warthe/Saale Cracovian
180-230 Interglacial Yarmouth Hoetting Holstein Sandomirian
230-300 Glacial Kansan Mindel Elster Jaroslavian
300-330 Interglacial Aftonian   Cromer Likhvin
330-470 Glacial "Nebraskan" Gunz   Menapian
470-540 Interglacial     Waalian  
540-550 Glacial   Donau II Weybourne  
550-585 Interglacial     Tiglian  
585-600 Glacial   Donau I    
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

changes in earth's axis tilt

Shape of Orbit + Precession

effects of eccentricity and precession

Where We Stand Now, And a Mystery

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.

The mystery. The roughly 100,000 year period of ice ages corresponds most closely to a 100,000 year cycle in the shape of the earth's orbit. Yet the variation in sunlight between January (perihelion) and July (aphelion) is trivial compared to the seasonal variations due to the tilt of the earth's axis, and the changes in distance from the sun are tinier yet. Nobody has yet figured out how the shape of the earth's orbit translates into climate change.

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.

Late Pleistocene-Holocene


Late Pleistocene in the Midwest

Man in The Great Lakes

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Created 20 January 1997; Last Update November 2, 1999
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