Fulgurites are glass tubes formed when lightning strikes a desert or beach. Artificial fulgurites are made by running a high-voltage arc through a tub of sand.
I started searching for fulgurites this morning after being reminded of a hoax image that went around last year. It purported to show a massive fulgurite on a beach but was, instead, a stick covered in wet sand. But, as Kyle Hill wrote at the But Not Simpler blog last July, the hoax doesn't make real fulgurite any less awesome.
Incredibly, lightning can and does in fact create something amazing when it hits sand, but the conditions have to be perfect. When it hits a sandy beach high in silica or quartz and the temperature goes beyond 1800 degrees Celsius, the lighting can fuse the sand into silica glass. The blast of a billion Joules radiates through the ground making fulgurite—hollow, glass-lined tubes with a sandy outside. Petrified lightning.
When the lightning perfectly strikes the sand, it branches through it like the root system of a tree to make this beautiful anomaly. But that simple fact is key to getting to the root of the viral photo: The lightning creates a tube of glass through the ground, not above it. You can actually see the impact hole when it occurs in rock.
