For hundreds of years humans relied on the compass for navigation. Even today compasses serve as a backup for advanced navigation systems found in aircraft and ships, which are based on satellites and sensors. The compass, a simple device composed of a metal needle attached to an axis, points to the magnetic north in the absence of external interference. Magnetic north was previously considered a stable and reliable base for navigation because it was thought to always point north. However, in the early nineteenth century the German scientist Alexander von Humboldt discovered that the Earth’s magnetic field does not always remain exactly in the same place, but is subject to fluctuations. Later additional evidence was found that confirmed his findings and strengthened our understanding of the magnetic field.
An even more surprising discovery occurred in the mid-twentieth century. The magnetometer, a device that measures the direction and strength of the magnetic field, developed by the United States military to detect enemy submarines during World War Two, recorded unexpected disturbances in the magnetic direction in certain ocean regions. These findings led to the understanding that the minerals composing the basalt rocks on the ocean floor carry the signature of the magnetic field that existed when they were formed millions of years ago. It became clear that the magnetic field underwent several reversals – and at certain times it pointed south.
Despite enormous progress in the development of navigation systems, the magnetic field is still important today for many navigation devices, making monitoring of field fluctuations especially important. Even if the fluctuations do not lead to a full reversal but only to smaller changes in the position of magnetic north, they can affect navigation and advanced electronic systems. Therefore, geological institutes in Britain and the United States publish an updated model of the current Earth’s magnetic field every five years.
The rotation of the Earth, combined with the movement of metal currents, causes the magnetic field to arrange in a unique form, like two lobes called magnetic lobes.
The question of the origin of the Earth’s magnetic field puzzled scientists for hundreds of years. Today we know it is the result of internal processes occurring deep in the Earth’s core, where currents of liquid metals in the outer core generate an electric field. A magnetic field is created when there is an electric current, and this physical phenomenon also occurs on a smaller scale, for example around electric wires.
Thus, the changes occurring in the metal currents dictate the changes that will be measured in the magnetic field above the Earth. Models simulating the flow of liquid metals in the Earth’s outer core succeed in illustrating the mechanism behind the formation of the magnetic field: the rotation of the Earth, combined with the movement of metal currents, causes the magnetic field to arrange in a unique form, like two lobes surrounding the Earth. The shape of the field can be mapped by connecting points where the field strength is equal, called contours or isofield lines.
About two decades ago researchers noticed that the Earth’s magnetic north drifts relatively quickly, from its location in Canada toward Siberia. Using simulations based on models of the Earth’s magnetic field, the effect of the two magnetic lobes on the boundary between the core and mantle under Siberia and Canada was examined. According to simulations conducted in the study, the lobes dictate the positions of the magnetic poles in these areas.
Between 1970 and 1999 it was discovered that the weakening of the magnetic field in the Canadian region was caused by changes in the flow patterns in the core beneath it, which led to the elongation of the Canadian lobe. At the same time, the Siberian lobe remained stable and even strengthened slightly, causing an increasing pull of magnetic north toward Siberia. According to the models, the trend is expected to continue in the next decade, with magnetic north drifting another 390 to 660 kilometers toward Siberia.