An expert from the University of South Florida deduced how big a bolt of lightning was based on the size of rocks formed by lightning.

When lightning strikes sand it creates a new type of rock, called fulgurite – a hollow tube formed as the lightning travels through the sand, vaporizing it and melting its outer edges.

Researchers determined that on average, the energy required to form these rocks was at least about one megajoule per meter of fulgurite formed.

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