Jul 25, 2023

Weather Wednesday: fulgurites

FARGO — If you’ve ever walked on a beach or sand dunes, whether that be in lakes country, the Great Lakes or an ocean coast, you may have walked over what some call “fossilized lightning”.

”Its what happens to sand when it’s struck by lightning,” Just like in the movie Sweet Home Alabama, when a lightning bolt strikes sand: underground art is formed, though the fragile formations aren’t quite as fancy as the movie depicts. Fulgurites, named after the Latin word for lightning: fulgur, are natural tubes or crusts of glass formed when lightning strikes sand, mostly composed of quartz.

50000 degrees Fahrenheit, that’s how much lightning heats up the air around it, roughly five times hotter than the surface of the sun. And when that heat hits the sand, the silica grains are fused together, creating a hollow tube that follows the path of the lightning bolt as it disperses into the ground.

The inside of the tube has a smooth, glassy surface due to the rapid heating and cooling of the sand as it solidifies. The outside is more rough, covered with partially melted sand grains, the color can vary greatly across the world due to the different composition of the sand.


Most fulgurites break as they are sifted out of the sand but the longest fulgurite found was excavated by researchers at the University of Florida in 1997. It has two branches, one measuring nearly sixteen feet and the other extending seventeen feet.

Fulgurites can also form on rocks and resemble branches or veins on the rock surface.