Land Ice

Part B: Glaciers on the Move

Despite their massive sizes and seeming permanence, glaciers are always on the move. Gravity pulls glacial ice downhill and causes it to deform under its own weight. As glaciers move across the landscape, erosion and deposition of soil, rock, and debris change the underlying surface. Past glaciers are responsible for many beautiful and sometimes strange geological features such as rolling hills in Ireland, fjords in Norway, and giant boulders in New York City's Central Park.

Most glaciers creep along at a pace that's too slow to detect with the naked eye (about a foot a day). But sometimes conditions are just right to cause glaciers to surgesurging glacier: a glacier that experiences a dramatic increase in flow rate, 10 to 100 times faster than its normal rate; usually surge events last less than one year and occur periodically, between 15 and 100 years. forward at speeds up to 100+ feet per day!

1. Read Background Essay: Fastest Glacier (Acrobat (PDF) 40kB Jul3 11) from PBS Learning Media.
   
2. Watch the Fastest Glacier video below (running time approximately 5 minutes). Take notes as you watch, so you are prepared to discuss the following questions with your classmates.
   • How fast does the Jakobshavn Glacier move compared to other glaciers?
   • What is the scientists' explanation for the increased speed of the Jakobshavn Glacier?

As you learned in the video, the speed of the Jakobshavn glacier dramatically increased from one foot per day to 113 feet per day, largely due to meltwater seeping underneath the glacier. Try this simple experiment for yourself. You'll need a small wooden block and an ice cube.

1. Slide a wooden block across a table or desk.
2. Next, slide an ice cube across the same surface.
3. Now try sliding the wooden block across a wet surface.

How Do We Know What We Know?

How do you measure the speed of glaciers? Watch the following video to learn about some of the different methods scientists use to figure out how fast glaciers flow.