Studies of ice cores in Greenland demonstrate that the last ice age ended abruptly 14,670 years ago. Figure 1 shows that temperatures rose 15 degrees Fahrenheit in just 50 years. Within the next few hundred years, the dust that blew into the ice from barren plains in front of the glaciers was replaced by nitrogen compounds formed by burning of the new forests.

During the glacial period, mountain valleys were filled by glaciers, and much of the northern hemisphere was covered by ice sheets. Many of the earth's modern landforms were formed by this process of glaciation and deglaciation. Some of the most dramatic features are shown in Figure 2 (toe of Rhone glacier), Figure 3 (modern Rhone valley), Figure 4 (valley in Beartooth Mountains), Figure 5 (Exit glacier), and Figure 6 (lake and talus pile in Banff National Park).

Figure 1. Summarized data from Greenland ice cores. (based on (Severinghaus, J.P. and Brook, E.J., 1999; Legrand, M. and Mayewski, P., 1997).

Figure 2. Toe of Rhone glacier retreating (melting) up the Valley of the Rhone River, Switzerland.

Figure 3. Valley of Rhone River that was formerly occupied by Rhone glacier, Switzerland).

Figure 4. Lakes in deglaciated valley in Beartooth Mountains of Montana.

Figure 5. Gravel in outwash plain in front of melting toe of Exit glacier, Alaska.

Figure 6. Glacial lake and rock debris (talus) in deglaciated valley, Banff National Park, Canada.

Ice sheet effects

Glacial and post-glacial features are more subtle where ice sheets covered the land surface away from mountains. The ice sheets normally flattened the landscape, both by erosion and dumping of debris from melting ice. This left hummocky terranes with "disrupted" drainage, commonly dominated by small lakes. Figure 7 shows a smoothed off landscape in the Orkney Islands, and Figure 8 shows similar features in North Dakota.

Figure 7. Glacially smoothed landscape in Orkney Islands.

Figure 8. Ponds in North Dakota.

Figure 9. Norwegian fjord.

The continental ice sheets extracted so much water out of the oceans that sea level fell about 400 feet below the present during maximum advance of ice sheets. On the eastern and Gulf coasts of North America, dry land extended 100 or more miles seaward from the present coastline. Sea levels rose rapidly as the glaciers melted and reached its present position about 7000 years ago. The rise in sea level flooded valleys and created fjords along mountainous coasts Figure. 9, Norway; Figure 10, eastern Greenland). Along flat coastal areas, rising sea levels filled valleys and left islands at the sites of former hills (Figure 11, Finland). In some cases the glacial melting thus created habitat fragmentaion.

Most recent interglacial

After this rapid warm-up, the earth entered an "interglacial", or warm, period that followed the end of the last glaciation. The climate change of the northern hemisphere is summarized in Figure 12, which is taken from "History and Environment of North Carolina's Piedmont)," with changes in vegetation in North Carolina on the right. (The term "Younger Dryas" signifies a time of renewed cooling that is recognized by the presence of pollen of Dryas plants in southern Europe).

Figure 10. Fjord in eastern Greenland.

Figure 11. Islands along Finnish coast.

Figure 12. Vegetation changes in North Carolina in the past 14,000 years.

Further Reading

• Severinghaus, J.P. and Brook, E.J., 1999, Abrupt climate change at the end of the last glacial period inferred from trapped air in polar ice. Science, v. 286, p. 930-934.
• Legrand, M. and Mayewski, P., 1997, Glaciochemistry of polar ice cores: A review. Reviews of Geophysics, v. 35, p. 219-243.