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This photograph shows how survey flags
are used to measure the flow rate of the Mathes Glacier
in Alaska. The glacier is moving from left to right
in this photograph. Eleven survey flags were pounded
into the surface of the glacier along a straight line
perpendicular to the glacier's flow. Only six flags
are visible in the image; the rest are too far away
to see. Using the change in position of the flags over
time, scientists can calculate the speed of the glacier.
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