Glaciers Then and Now

Teri Eastburn, Lisa Gardiner, Windows to the Universe/UCAR SciEd

In this activity, students compare two photographs (with time spans of 30-100 years between photos) of specific Alaskan glaciers to observe how glaciers have changed over the time interval. Activity is a good kickoff for learning about glaciology - how and why glaciers form, grow and shrink, and their relation to climate change.

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Notes from our reviewers

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Students would be likely to learn more from the activity and be better able to respond to the discussion questions if they did their own investigation of the nature of glaciers worldwide, using the resources provided at the end of the activity. Targeted to grades 4-8, but educators should adapt accordingly; older students will need to do more than compare photographs.
The background information on glacier formation is minimal and needs to be supplemented by the educator. Includes a very illustrative documented series of glacier images that provide a good general exposition of glacier change. Activity looks at glaciers in Alaska, but discussion questions appear to apply to glaciers globally, making the assumption that what is happening in Alaska is happening everywhere - should be supported by some additional materials. Comment from scientist: "Continental Glacier" is equated with "Ice Sheet" in the activity, which is not quite correct. "Continental Glacier" is an ambiguous term, and although it is used as a synonym for ice sheet (e.g. in the Wikipedia entry on glaciers), it also refers to a glacier of any size located in a continental environment (as opposed to a maritime environment). It's suggested educators drop this term. Another error: iceberg calving is not listed among the causes of glacier retreat. Most of the photo pairs shown here depict retreat due to calving. Comment from scientist: The educator should introduce the concepts of accumulation (see paragraph 2) and ablation (or loss), and then present growth and decay (or advance and retreat) as the balance between these. The text only describes accumulation and retreat and doesn't emphasize that glaciers can exist in a steady state. Comment from scientist: For advanced classes, the educator could also describe the distinction between retreat by climatically-controlled mass balance (i.e. accumulation vs. melt, primarily) and retreat by calving, which can be quite independent of climate forcing. This would be an arcane point far beyond the level of the activity, except for the fact that 5 of the 8 photo pairs show calving retreat. Calving retreat is far more complex than simple melt.
Visual comparisons of changes in glaciers over time is dramatic evidence of environmental change and a good basis for examining possible causes. Activity provides students with the opportunity to investigate for themselves the nature of glaciers. A good set of assessment questions at the end of the activity.