I had previously blogged on this site about my personal discovery that the Dominican black sand is in fact lodestone ground into sand by the sea’s action. Lodestone is formed when the earth’s polar magnetic field magnetically-charges particles in magma from deep within the earth and the magma emits from a volcano and cools before it can un-align, so it remains magnetic.

Now, the World Digital Magnetic Anomaly Map (WDMAM) shows the variation in strength of the magnetic field after the Earth’s dipole field has been removed. Earth’s dipole field is generated by circulating electric currents in the planet’s metal core. It varies from 35,000 nanoTesla (nT) at the Equator to 70,000 nT at the poles. Notice the red shading along the Eastern Caribbean “spine” of islands.

This post was guest blogged by Dan Tanner

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