Resource: Antarctic Ice Movement: Part II

Antarctica's extremely cold and dry climate preserves its immense, domed ice sheet as snow slowly collects atop the glacial ice. Because the weight of the snow and ice at the top of the dome is so great, gravity forces the ice to spread outward down slope. The rate of movement varies from less than a meter per year near the dome to several hundred meters per year near the edges. Eventually, the glacial ice runs into the sea, forming floating platforms called ice shelves.

The speed with which an ice sheet moves depends on a few variables, including the thickness of the ice and the pitch of the slope on which it lies. Speeds may also vary along different parts of an ice sheet. Ice streams are well-defined areas up to several kilometers wide where rapid ice flow occurs. They typically run from the dome of the sheet out onto the ice shelves and can travel at speeds of up to a kilometer per year, which is roughly 100 times faster than the surrounding ice.

Under normal conditions, an ice sheet is frozen to the bedrock, which significantly slows its movement down slope. Some glaciologists, however, believe that higher temperatures at the base of the ice produce a film of water and mud that separates the ice from the bedrock to form an ice stream. What might be causing this rise in temperature? Possible explanations include the immense pressure of the overlying ice and areas of volcanism under the ice sheet. A third potential heat source is atmospheric warming. Although recent human activities might be to blame, it could also be possible that the increased atmospheric heat following the end of the last ice age has only now penetrated to the base of the thick ice.

Recent studies suggest that Antarctic ice is flowing out to sea faster than it accumulates on land. This is especially the case on the West Antarctic Ice Sheet, much of which lies on land depressed below sea level. Because ice in direct contact with seawater is subject to faster warming, the extensive ice shelves of the West Sheet, where sea temperature has risen by 4.5°C in the past 50 years, could precipitate the collapse of the entire sheet. The amount of water contained in the West Sheet could raise the global sea level by 6 meters.

To learn more about ice sheet movement, check out Antarctic Ice Movement: Part I.

To learn more about how glacial melting might affect global sea level, check out Mountain of Ice: If the Ice Melts and Antarctic Ice: Sea Level Change.

To learn more about the important roles that ice plays in moderating global temperature and ocean circulation, check out Earth System: Ice and Global Warming.

To learn more about the challenges that scientists face who work in Antarctica, check out Antarctica: A Challenging Work Day.

• Describe the phenomenon that is presented at the beginning of the video.
• Why is it important to understand the ice streams and whether they are going faster or slower? The video gives an excellent example of scientific method.
• Explain the hypothesis that the geologist developed to explain the phenomenon, and describe the experiment that the scientists conducted that provided evidence to support the hypothesis.
• How did technology confirm the scientist's prediction that there was mud beneath the ice streams?
• Explain the hypothesis for the melting of the glacier bed.