The natural remanent magnetism of the andesitic lava of Mt. Utsukushi-ga-hara in the Central Part of Japan, showes that both its intensity and direction are too scattered to be considered as normal. This anomalous magnetisation is supposed to come from the magnetisation owing to the momentary strong magnetic field afforded by thunderbolts. The writers have measured the relations between the demagnetisation and magnetisation of samples in a strong magnetic field. The result seems to support their assumption.
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Matsuzaki et al. (1954) studied this question.