Fulgurites: What Happens When Lightning Strikes Sand?
A thin, rough tube in the sand may look like an old root. Sometimes it records a very different event: a lightning strike. Glass formed this way is called a fulgurite.
How lightning makes glass
When lightning travels through sand, it releases intense heat along a narrow path. Some material can vaporise, while nearby sand melts. As the melted material cools, it forms glass around the path of the strike.
At Great Sand Dunes National Park in the United States, this process produces dark glass tubes. Their shape follows the lightning's route through the ground.
Why the outside looks rough
The outside can carry grains of sand, so the object may look more like a sandy twig than a shiny piece of glass. A broken end may reveal the hollow interior. These delicate tubes can break easily.
What a find can tell you
A confirmed fulgurite is evidence of a lightning strike. A tube shape alone, however, is not enough to identify an unknown object. Photograph the surface and any naturally exposed end, rather than breaking it to check.
At protected sites, leave specimens where they are. If thunder approaches while you are exploring open sand, stop looking for rocks and seek shelter. A fulgurite is an interesting reminder of how quickly lightning can change the ground.
Source: National Park Service: Fulgurites—The Power of Lightning.
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