2 December, 1996

Today was another collecting day at Cape Chocolate. The Cape is a very distinct geographic feature that is easy to spot by helicopter. The melt pools, however, are several miles north of the Cape in a place where everything looks the same. The topography is a series of hills and valleys with no unique features except for Mount Erebus across the Sound to the Northeast. I decided that an easy way to identify collection sites would be with a series of compass bearings relative to the place where the helicopter left us. My first surprise came when I looked at the compass and saw Erebus to the Southwest. For a moment I thought the pilot had dropped us off at the wrong place. After looking at the map again, it began to make sense. The magnetic declination where we landed was 150 degrees East.

The cause for the confusion was there are actually two South Poles. One is the geographic pole, which is the axis of the Earth's rotation. The other is the geomagnetic pole, the place where the magnetic field is vertical up and down. If you were standing at the geomagnetic pole with a compass that could rotate in any direct, it would point toward the ground. The geomagnetic pole wonders, it's currently more than a thousand miles from the true South Pole. I've included a map which shows its path as its wondered from 1600 to 1980. The square on the map is Cape Chocolate. The arrow labeled A, which starts at the geographic pole and goes through the square, points to the geographic north pole or true north. The arrow labeled B, which starts at the geomagnetic South Pole and goes through the square, points to magnetic north. The two lines make an angle of about 150 degrees, which is the magnetic declination. If I had followed the compass needle north, I would end up going south.


The magnetic south pole is 1000 miles north of the geographic pole.


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