Glacial Retreat: Quantifying Changes in Glacier Cover Over Time
In this activity, you will use satellite images from the NASA Landsat team to quantify changes in glacier cover over time. This lesson utilizes change pair images of Bear Glacier in Kenai Fjords National Park, located on the southeastern portion of Alaska’s Kenai (pronounced: Key-nigh) Peninsula, bordering the Gulf of Alaska.
To enable students to analyze changes in glacier cover over time using satellite images.
NASA Phenomenon Connection
Satellite images provide scientists aerial views of glaciers, and a major source of these images has been provided by the Landsat Program. The Landsat Program is a series of Earth-observing satellite missions jointly managed by NASA and the U.S. Geological Survey. Since 1972, Landsat satellites have collected information about Earth from space by taking specialized digital photographs of Earth’s continents and surrounding coastal regions. The Landsat program has been collecting images for over three decades, enabling people to see and study the dynamic changes caused by both natural processes and human practices. One way to evaluate these changes is to compare images of a single area over an extended period of time. Two satellite images taken at different times of the same location are called change pairs and are frequently used by glaciologists to evaluate changes in a glacier.
The following materials are available to download and print:
• Glacier Retreat worksheet for each student
• Cover change grid for each pair of students - You will need to transfer the ready-made grid to a transparency sheet.
• NASA Landsat images for each pair of students
The following materials need to be acquired:
• Transparency sheets
• Markers with fine points for writing on transparencies
We highly suggest that the NASA Landsat Images of Bear Glacier be printed out in color and laminated. Color images facilitate the differentiation of glacier cover from land cover, and laminating the satellite images allows them to be used more than once.
Along the coastline of the park, glaciers have cut deep valleys into the mountains. As the glaciers retreat, these coastal valleys are filled with seawater, creating fjords. Changes in precipitation have caused Bear Glacier to recede. As glaciers recede, they leave behind rock and debris, which is called a moraine. Bear Glacier, as it retreated, paused long enough to build up a sizeable moraine. In fact, the beach in front of Bear Glacier is an old recessional moraine that has cut off Bear Glacier’s access to the tidewater’s edge. As a result, Bear Glacier, once classified as a tidewater glacier, is now a terrestrial glacier.
Glaciers are retreating not only along Kenai Fjord ’s coast but all throughout the park. In fact, most of Alaska’s estimated 10,600 glaciers are melting. Monitoring the glaciers can help determine why they are retreating. Glacier-monitoring efforts in national parks provide valuable information to park managers, as well as to the scientific community at large, about the effects of regional and global climate change. However, direct observations of glaciers are often difficult because they exist in cold, Polar Regions or high mountain areas that are inaccessible or inhospitable to humans. Furthermore, ice sheets and ice caps are so huge and change so slowly that repeated measurements are needed over large areas and long periods of time. Until recently, glaciologists had no accurate means of seeing the aerial extent of glacier ice on Earth.
1. Together with your partner, visually identify the areas in each image that are covered by Bear glacier.
a. Be careful not to include the icebergs floating in the lake or snow that has collected in the mountains that is not part of the glacier itself.
2. Place the transparency with the cover change grid over the image from 1986, and tape the corners of the transparency to the image. EXAMPLE
3. One partner will hold the image while the other partner outlines the glacier cover on to the transparency with a colored marker.
a. It is very important to distinguish between the glacier and the clouds, therefore, an option for this activity is to trace around only the long extension of the glacier (see outline example on the right).
4. Make a legend for your transparency cover change grid, which is now becoming a glacier cover map (see example map and legend to the right).
5. Place the transparent glacier cover map you just made over the 2002 image of Bear Glacier and tape the corners to hold it in place.
6. Using a different color of marker than you used in step 3, trace the outline of the 2002 glacier on the transparency grid.
7. Count and record the number of grid squares representing a change in glacier cover. It will take both partners to do this:
a. One partner will compare the transparency map to the 2002 satellite image and identify the grid squares that show glacier change. You may notice that some squares contain land that is only partially covered by the glacier. In this case, the most dominant cover type should be used.
b. The other partner will mark the equivalent changed squares using the Cover Change Grid. Work from the upper left to the upper right across each row, putting a dot in each square that represents a change in glacier cover.
8. Once you have determined how many grid squares represent a change in glacier cover, you will use this information to calculate the percent cover change in the satellite images provided of Bear Glacier.
9. Your teacher will ask for everyone’s results and then list them on the board. Write them down and then use them to calculate the class average.