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January 2001

November 2001

Example of digitising the lower part of the glacier  
 
Now the crevasses you digitised on the January image are superimposed on the November image. You will note that the digitised lines are not on the crevasses you selected. This difference is due to glacier movement. You can measure it using the Measure Tool: Image > Measure Tool. Don’t forget to set the Units in the Measure Tool menu bar to Meters and Pixel Size to 15m.

Note your measurements in a table.
 
 

Glacier part Displacement Jan – Nov 2001 Lower part 61 m, 47 m, 45 m, 67 m; average: ... (example) Middle part ... Upper part ...

 
 

- The ice movement observed must be larger than the pixel size of the sensor used (here it is of 15 m). Movement cannot easily be detected if it is smaller than that.
- There have to be clear features on the glacier that can be tracked during the period of observation (e.g. crevasses or rocks).
- Snow cover on one or both of the images prevents us from measuring displacement because snow contains no suitable features with sufficient contrast.

The magnitude and direction of glacier flow is important in order to understand glacier dynamics and glacier reaction to climate change. It is easier to estimate the development of glacier contact lakes when we know more about the glacier flow into the lake. When more than two repeat images are used, variations in glacier flow can be observed. Such variations may be linked to climatic influences, such as changes in glacier mass balance.
 
 

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