Alpine glaciers, also called valley glaciers, are found in high mountain valleys worldwide. At lower and warmer latitudes, they occur only at very high altitudes. At higher latitudes, closer to the Poles, they can occur in mountains at lower altitudes too. Glaciers that cover large areas of land and are not confined within valleys are known as ice sheets.
Alpine glaciers are responsible for carving mountains into distinctive shapes leaving pointed ridges between glaciers, u-shaped valleys where the glacier moved through, and hills of rock debris called moraines that were carried in, and pushed by, the glacier. Today, because of rapid global warming, alpine glaciers that are at tropical and mid-latitudes are melting very quickly. Many high latitude glaciers are also in retreat.
Snow that falls on a glacier may eventually become part of the glacial ice. The snowflakes become buried under more and more snow, eventually changing their shape because of the pressure from the layers of snow above and becoming part of the ice. Over time the ice crystals become so closely packed that the tiny pockets of air between them are squeezed out and the ice changes in color from white to blue.
Glaciers are not just giant ice cubes. All that ice can be a powerful force. Glaciers move over time scraping rock from the Earth's surface, bulldozing boulders, gravel, and sand into hills called moraines, and sending ice out over the ocean in massive ice shelves.
Under the pressure of its own weight, glacial ice flows downhill over time. The same is true of the flubber in this model. There are two main ways that this happens: (1) by internal deformation and (2) by basal slip.
Internal deformation: The ice moves plastically when under pressure from ice above. Weak bonds between the molecules in the ice allow layers of molecules to slip past each other. So, while glacial ice is a solid, over a long time it flows slowly like honey.
Basal slip: Glaciers also move downhill by sliding at their base. This process is called basal slip. Basal slip can be affected by friction at the base of the glacier. Basal slip can be enhanced if there is water at the base of the glacier. Pressure on the ice that is at the bottom of a glacier can cause some of that ice to melt producing a slippery little layer for the rest of the ice to slide upon. Also, there is evidence from Greenland that melt water can make its way from the top surface of the glacier to the bottom through tunnels in the ice called moulins.
Flubber is a polymer that has the properties of both a liquid and a solid. The molecules in the flubber are loosely arranged and can slide past each other.
If you find that your flubber mixture is too liquid or too solid, you can vary the ratio of glue to Borax. More glue will make the flubber more solid. More Borax will make the flubber more liquid. Make sure that the ratio that you use is consistent for all student groups to eliminate an unwanted effect of different varieties of flubber when students experiment during the second part of this activity.