With more than 29 million cubic kilometers (7 million cubic miles) of ice and snow, the Antarctic Ice Sheet is so massive that its weight depresses the underlying crust by 900 meters (nearly 3,000 feet). New snow that collects on the ice sheet's surface causes the ice beneath it to spread out and move along the slope of the land. In this video segment adapted from NOVA, a team of glaciologists carves into one glacier on the East Sheet to monitor the nature and speed of its movement.
Glaciers form over hundreds of thousands of years atop land in cold climates where snow and ice remain year-round. As snow layers accumulate, their weight forces underlying snowflakes closer together, thereby reducing the air spaces between them. The individual flakes crystallize and combine with other crystals around them to become glacial ice.
The largest glaciers, called continental ice sheets, blanket more than 50,000 square kilometers of land in ice and snow thousands of meters deep. Today, continental ice sheets are found only in Greenland and Antarctica. Divided into two unequal parts by a mountain range, the 14-million-square-kilometer Antarctic Ice Sheet alone contains about 70 percent of Earth's fresh water supply. The larger, eastern part rests entirely above sea level and covers Greater Antarctica. Most of the smaller, western part rests on rock at or below sea level and covers nearly the entire island archipelago collectively named Lesser Antarctica.
As more and more snow collects on an ice sheet and turns to ice, it forms a slight dome. The weight of the ice at the top of the dome becomes so great that gravity causes the underlying ice to slowly deform and spread 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 ice flows into the sea, forming floating platforms called ice shelves.
To better understand both the nature and speed of ice sheet movement, glaciologists look for evidence within the ice sheets themselves. One particularly instructive type of movement, shearing, occurs when adjacent planes slide past one another at different speeds. Evidence of shearing tells scientists that although the ice sheet's entire mass is in constant motion down slope, its upper part moves faster than its lower part. This happens because the base of the ice sheet is actually frozen to the bedrock.
Studies show that in Antarctica, both the top and bottom of the West Sheet are moving much faster in places than the East Sheet. This is significant because, if the entire West Sheet were to slide into the sea, it would raise the global sea level by 6 meters.
Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
We assign reference terms to each statement within a standards document and to each media resource, and correlations are based upon matches of these terms for a given grade band. If a particular standards document of interest to you is not displayed yet, it most likely has not yet been processed by ASN or by Teachers' Domain. We will be adding social studies and arts correlations over the coming year, and also will be increasing the specificity of alignment.