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Fulgurites are glassy, root-like tubes formed when a lightning stroke terminates in a dry sandy soil. The intense heating of the electrical current passing down into the soil along an irregular path fuses (melts) the sands. Concurrently, vaporization of soil moisture and possibly even vaporization of the sandy materials, causes the molten material to be expanded into a tube whose diameter may be well over an inch, but whose wall is very thin. Fulgurites have been recovered in lengths of over five feet.
The fulgurites pictured below were discovered just north of Aberdeen, South Dakota by rural firefighters who noticed a "glowing hole in the ground" after a round of severe thunderstorms. Thanks to former Brown County Emergency Manager Jesse Luce for bringing these amazing samples to our attention.
If lightning is hot enough to melt sand, what do you think it can do to you? ALWAYS take cover when lightning is in the area!