EarthLabs > Climate and the Cryosphere > Lab 5: Evidence of Recent Change > 5A: Melting Glaciers

Evidence of Recent Change

Part A: Melting Glaciers

Visit the world's high mountain ranges and you'll see less ice and snow today than you would have a few decades ago. More than 110 glaciers have disappeared from Montana's Glacier National Park over the past 150 years, and researchers estimate that the park's remaining 37 glaciers may be gone in another 25 years. Half a world away on the African equator, Hemingway's snows of Kilimanjaro are steadily melting and could completely disappear in the next 20 years. And in the Alps, glaciers are shrinking (and disappearing) every year, much to the dismay of mountain climbers, tourist agencies, and environmental researchers.

Visualizing Change

Looking at photographs taken several years apart is a great way to spot signs of change. Glacier photo pairings demonstrate that glacier positions can change dramatically, even over a relatively short period of time (geologically speaking).

  1. Click "Begin" to launch the Documenting Glacial Change interactive below. Look at each pair of images and observe the different landform features. What changes do you see?

    This content is available in flash format only

    Courtesy PBS Learning Media.


    Stop and Think


    1: Describe some of the changes that occur on a landscape when a glacier shrinks. Consider the impact on both the land and on living things.


Measuring Change

Gangotri Glacier is one of the largest in the Himalayas, and is the source of the Ganges Riverthe most sacred river in Hindu culture and a lifeline for millions of people who rely on it for their daily needs. The fertile soil of the Ganges basin is vital to the agricultural economies of India and Bangladesh.

  1. Download the image below of the Gangotri Glacier by right-clicking on the image (Mac users press ctrl-click) and choosing the appropriate "save as" choice from the menu. Save the file in an obvious place such as your Desktop or Downloads folder.
    Gangotri Glacier
    This composite ASTER image shows how the Gangotri Glacier terminus has receded since 1780. Contour lines are approximate. (Image courtesy of Jesse Allen/ NASA Earth Observatory; based on data provided by the ASTER Science Team; glacier retreat boundaries courtesy of the Land Processes Distributed Active Archive Center, USGS.


  2. If you already have ImageJ on your computer, move on to the next step. If your computer does not have ImageJ, you will need to install it now.
    1. Open the ImageJ download page.
    2. On the download page, click the link that appears directly below the name of your computer's operating system (e.g. Mac, Windows, Linux). This action will transfer a compressed file of the software to your computer. Your browser should automatically expand the file, creating an ImageJ folder on your computer's hard drive.
    For more details, or if you have problems running the application, access ImageJ's Installation Instructions then select your operating system.
  3. Launch ImageJ and open the Gangotri Glacier image file by choosing File –> Open... and navigating to where you saved the image.
  4. Set your measurement options.
    • Choose Analyze > Set Measurements... to open the Set Measurements window.
    • Check the boxes for Area and Perimeter (length). Then click OK.
      Analyse set measurements lgr
  5. Set the scale for the image using the scale bar at the bottom left of the Gangotri Glacier image. If you measure distances or areas on a digital image, without first setting the scale to "real world" units, your measurement results will be expressed in pixels and square pixels.
    • Use the straight line selection tool Straight line selection tool to drag out a line across the scale bar. TIP: Hold down the Shift key while drawing your line to keep it perfectly horizontal. You may also find it useful to zoom in on the image before drawing your line.
    • Choose Analyze > Set Scale... to open the Set Scale window. The distance you measured in pixels will be displayed.
    • Enter 1 for the Known Distance and km or kilometers for the Unit of Length. To redo your line, click on the arrow tool, then re-click on the line selection tool. This effectively resets the tool.
    • Click OK
      • Using the straight line selection tool Straight line selection tool , click on one end of the scale bar, drag to the other end of the scale bar, and click again. TIP: Hold down the Shift key while drawing your line to keep it perfectly horizontal.

        Glacier Set Scale
      • Choose Analyze > Set Scale...

        analyse set scale drop down
      • The Set Scale window opens. The distance you measured in pixels will be displayed. In this case, we got 67.125 pixels. Your value may not be exactly the same, but it should be close to this. Enter 1 for the Known Distance and km or kilometers for the Unit of Length.
      • Click OK.

        Glacier Set Scale Window
  6. To check the scale you set, use the straight line selection tool Straight line selection tool to drag out a line across the scale bar again. Choose Analyze > Measure. You should get something very close to 1 km in the Results window. If you don't, reset the scale.
    • Using the straight line selection tool Straight line selection tool , click on one end of the scale bar, drag to the other end of the scale bar, and click again. TIP: Hold down the Shift key while drawing your line to keep it perfectly horizontal.

      Glacier Set Scale
    • Choose Analyze > Measure.

      analyse measure drop down
    • The Results window opens. You should get something very close to 1 km. If you don't, reset the scale.

      Measurement Results Window

  7. Measure how far the terminus of the glacier receded between 1780 and 2001.
    • Using the straight line selection tool, click on the blue contour line for 1780, drag to the blue contour line for 2001, and click again.
      Measure Terminus Recession
    • Choose Analyze > Measure.
    • Record your result.
  8. Measure the area lost by the Gangotri Glacier between 1780 and 2001.
    • Using the freehand selection tool Freehand Selection Tool , carefully trace the area inside the contours for 1780 and 2001.
      ImageJ Toolbar



      Area Selection
    • Choose Analyze > Measure.
    • Record your result.
  9. Answer the Stop and Think questions below.

  10. Stop and Think


    2: How far did the terminus of the Gangotri Glacier recede between 1780 and 2001?

    3: How much area did the Gangotri Glacier lose between 1780 and 2001?

    4: What is the average rate of recession of the terminus of the Gangotri Glacier? Express your answer in meters/year.

    5: Scientists have measured mass balance on more than 300 glaciers since 1946. Based on continuous observations of 40 of those glaciers, the cumulative change in glacier thickness from 1961-2005 was found to be approximately -12 meters. This 12 meter decrease in glacier thickness is equivalent to about 9,000 km3 of meltwater.

    1. Altogether, the world's rivers contain 2120 km3 of water (Source: USGS). How does this compare to the amount of water generated by thinning glaciers between 1961 and 2005?
    2. Using the conversion 1 km3 = 2.64 x 1011 gallons, calculate the amount of water in gallons generated by thinning glaciers between 1961 and 2005.
    3. It is estimated that the Great Lakes contain about 6 quadrillion (6 x 1015) gallons of water (Source: Great Lakes Information Network). How does the amount of water generated by thinning glaciers compare?

    6: Scientists typically calculate glacial mass balance on an annual basis. Explain why it doesn't make sense to perform this calculation more or less often.

    7: What impact does climate change (warming or cooling) have on the balance between glacier inputs and outputs?


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