Lightning-induced remanent magnetization—the Vredefort impact structure, South Africa

Research at the Vredefort Dome, a UNESCO World Heritage Site and one of Earth's largest meteorite impact structures, reveals that lightning strikes can significantly enhance natural remanent magnetization (NRM) in target rocks. Laboratory experiments demonstrated increased NRMs, susceptibility, and Koenigsberger Q values in both Vredefort and non-impact Johannesburg dome rocks after simulated lightning pulses. Magnetic measurements and scanning electron microscopy identified mineralogical changes, including the oxidation of magnetite to maghemite, grain fragmentation, and size reduction—processes analogous to those observed in lodestones. These findings suggest that lightning-induced magnetization could explain elevated Q values previously attributed solely to meteorite impact or plasma fields, offering new insights into the magnetic properties of impact structures.

Salminen, J., Pesonen, L. J., Lahti, K., & Kannus, K. (2013). Lightning-induced remanent magnetization—the Vredefort impact structure, South Africa. Geophysical Journal International, 195(1), 117–129. https://doi.org/10.1093/gji/ggt230