The Laschamp event was a short reversal of the Earth's magnetic field. It occurred 41,400 (±2,000) years ago during the last ice age and was first recognised, in the late 1960s, as a geomagnetic reversal recorded in the Laschamp lava flows in the Clermont-Ferrand district of France. The magnetic excursion has since been demonstrated in geological archives from many parts of the world. The period of reversed magnetic field was ~440 years, with the transition from the normal field lasting ~250 years. The reversed field was 75% weaker whereas the strength dropped to only 5% of the current strength during the transition. This resulted in greater radiation reaching the Earth, causing greater production of beryllium 10 and higher levels of carbon 14.
- Bonhommet, N.; Zähringer, J. (1969). "Paleomagnetism and potassium argon age determinations of the Laschamp geomagnetic polarity event". Earth and Planetary Science Letters 6: 43–46. doi:10.1016/0012-821x(69)90159-9.
- Helmholtz Association of German Research Centres (16 October 2012). "An extremely brief reversal of the geomagnetic field, climate variability and a super volcano". Retrieved 19 October 2012.