Currents in the Earth and under the sea
Stories from Physics for 11-14 14-16
Telluric currents are natural or artificial currents that flow through the Earth or the sea. They have many causes including changes to the Earth’s geomagnetic field.
Michael Faraday unsuccessfully attempted to measure telluric currents from Waterloo Bridge using suspended electrodes. Undeterred, he obtained permission from the king to place electrodes into the lake in the gardens of Kensington Palace. He initially detected a small current, but concluded this was due to the thermoelectric effect.
In addition to the intended signals, currents are induced in undersea cables by a number of mechanisms. Some of the currents fluctuate over the solar day because of variations in the ionosphere caused by changes in solar radiation. Others are induced by the tidal motion of the oceans which results in a movement of ions in the Earth’s magnetic field. In addition, currents may be driven in long cables that run north-to-south by a thermoelectric effect due to temperature differences along the cables.
Finally, the detonation of a high-altitude nuclear bomb is reported to have caused disturbances in the Earth’s radiation belts and geomagnetic field that induced detectable currents in undersea cables.