A swirling vortex of molten rock has been found 3,000 km beneath the North Pole. It is believed that the Earth's magnetic field is generated by circulation in its molten outer core. After studying the historical measurements of the magnetic field, geophysicists Peter Olson and Jonathan Aurnou of the John Hopkins University in Baltimore, Maryland, USA, traced a flow, "which has the structure of a giant hurricane' ( New Scientist , Vol 164, No 2212).