Insights on lightning-induced remanent magnetization from high-current impulse experiments

Lightning strikes can induce strong and complex remanent magnetizations in rocks, potentially overprinting their natural paleomagnetic record. To investigate the mechanisms and outcomes of lightning-induced remanent magnetization (LIRM), we conducted controlled high-current impulse experiments on mafic and ultramafic rocks using the lightning generator of the High Energy Laboratory at the University of São Paulo. Peak currents up to ~80 kA with waveform reversals were applied to cylindrical specimens from Trindade Island basalts, Vista Alegre tholeiites, Planalto da Serra alkaline basalts, and Quatipuru peridotites. Magnetic susceptibility, hysteresis, FORC diagrams, and Lowrie–Fuller tests were measured before and after the experiments. Results show that lightning-like currents increase remanent magnetization in most lithologies, with some specimens exhibiting >400% enhancement, and REM ratios (NRM/SIRM) rising above 0.1, consistent with natural fulgurites and lodestones. Importantly, waveform polarity reversals produced opposite magnetization directions between nearby and more distant specimens, resulting in the coexistence of two components of remanence within tens of centimeters of distance from the striking point. Quatipuru peridotites, which are predominantly paramagnetic, exhibited distinct behavior, including susceptibility decreases and an enhanced frequency-dependent response, suggesting the formation of superparamagnetic grains. These findings demonstrate that lightning discharges can significantly modify the magnetic properties of rocks. Lightning-induced changes provide diagnostic signatures, amplifying their remanence in orders of magnitude while generating complex directional patterns, which complicate paleomagnetic interpretations. Plain Language Summary Lightning strikes can strongly affect the magnetic properties of rocks. When this happens, the new signal may hide or distort the original record of Earth’s magnetic field. This is important because paleomagnetism is one of the main tools used to study the history of the planet’s interior and surface. In this study, we simulated lightning in the laboratory with currents as high as 80,000 amperes. We applied these pulses to volcanic and mantle rocks from Brazil and measured their magnetic properties before and after the experiments. The results show that lightning can increase rock magnetization by several times, change the direction of magnetization over short distances, and even create very small new ferromagnetic grains. These findings demonstrate that lightning can leave strong and complex magnetic imprints on rocks, which must be recognized to avoid misinterpretation of paleomagnetic records on Earth and other planets.