# Measuring Glacial Retreat

## Activity Source:

Adapted with permission by U.S. Geological Survey.

The USGS has been studying glaciers in Glacier National Park since 1850. It is estimated that there were 150 glaciers in the park back then, and when the national park was established in 1910. Today only 25 glaciers remain.

Scientists go back every year to repeat photographs, as well as to examine the ice and the ecology of the landscape to see how glacial retreat is affecting plant and animal species that live there.

Climate change is affecting alpine glaciers worldwide. Studies such as the ongoing monitoring at Glacier National Park can help scientists understand the rate and the effects of these changes.

## Procedure (for teacher)

1. Look at the USGS Repeat Photo Gallery or the National Geographic video. Ask students to note their observations. Help them distinguish between an observation and an interpretation.
2. Using multiple copies of the map, have students cut out or trace Grinnell Glacier at different times.
3. With students, measure the extent of the glacier at different times by laying the cutout or tracing over graph paper and counting the squares. Decide how you are going to count partially covered squares, and discuss how that affects the data.
4. With more advanced students, you might want to think about glacial thickness as well. Ultimately volume is more important than surface area. Ask students how they would estimate the volume of the glacier. What information would they need, and where could they get it?
5. Make a plot of glacial extent vs. time. Draw a line that best describes the change. Is it linear? Exponential? Is the rate of change the same, or does it vary through time? If the rate is changing, is glacial retreat happening faster or slower than it used to?
6. Use the plot to make a prediction: When will Grinnell Glacier completely disappear?
7. Discussion can be far-ranging, based on grade level and learning goals, regarding the science of climate change, the processes of glacial growth and melting, and the method of measuring glacial retreat used here.

## NGSS 3-D Learning

• Science and Engineering Practices ─ Analyzing and Interpreting Data
• Disciplinary Core Ideas ─ Earth and Human Activity
• Crosscutting Concepts ─ Stability and Change