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Ice Velocites

The surface velocities of a glacier can be measured quite easily using GPS. This was first demonstrated in 1874 by placing stakes in a straight line across the glacier and then coming back later and observing there change in position. This meathod is still used today, execpt that with GPS acurate to withing a few centimeters it can be done in a matter of days instead of years. The change in position over the change in time equals the velocity of the ice on the surface of the glacier.

This method gives us the velocity of the ice on the surface of the glacier. If we want to know how much ice is flowing through a cross section of a glacier we need to know how fast the ice is flowing throughout the glacier. Through a serires of equations that relate ice velocities to density, gravity, slope of the glacier, and the temperature of the ice Paterson was able to show that the mean velocity of a cross-section is within a few per cent of the mean surface velocity.