Compasses also behave erratically in the Bermuda Triangle. If you pass through any of its three borders, the aberrations will not cease instantaneously, but these reported electromagnetic aberrations can be plotted on a map with a center squarely in the Triangle.
One or two mariners over the centuries could be referred to entry #10, but several thousand maritime travellers, in vehicles from small boats to large ships and airplanes, have complained of being unable to rely on their compasses during sections of their journeys through the Triangle.
It is open ocean, and no submerged anomalies have ever been reported. The sea floor has been completely mapped with sonar. Shipwrecks and plane wrecks are not magnetic, and have no bearing on compasses.
Whatever causes the electromagnetic disturbances affects compasses very rarely, but there are many reports of needles intermittently spinning or spiking.
It's easy enough to navigate via the sun or stars, provided they're visible, but the aberrant behaviour of compasses remains a mystery, and a likely cause of at least some of the disasters.
