Posted March 24, 2014
Congrats to Bob, Dale, and Sarah who all knew that this is fulgurite, also known by some as “petrified lightning”! Fulgurites occur when lightning strikes sand or soil, and instantly fuses the substrate into glassy tubes. The lightning has to be very hot too, at least 1800 degrees C (3270 degrees F). That’s hot! In this case, the lightning hit sand on a beach or desert and formed these tubes in the shape of the electrical current. The outside of these tubes has a rough sandy appearance and is made up of grains of sand fused by the heat. The interior of the tubes is smooth and glassy and sometimes is lined with small bubbles. Fulgurites can vary in size but generally can be as long as about 15 feet. But Charles Darwin recorded one in Cumberland, UK as long as 30 feet! Fulgurites can also form when high voltage cables fall and land in a sandy surface.
Notice how the bottom half of the fulgurite in the lower right of our picture (above) resembles the fulgurite in the photo from Wikipedia (left)!
They can be found around the world and have been recorded on beaches, in deserts, and sand dunes. A different type of fulgurite can form when lightning strikes solid rock, such as on top of a mountain, where it can leave a beautiful glazed pattern or crust on the rock. I once saw a lightning bolt strike right in front of me when hiking near the barren summit of Mt. Whitney in California (good thing that I’m a slow hiker!). Fulgurites of various sizes have been reported as relatively common on or near rocky mountaintops in the western United States. From now on, these fulgurites are as close as I want to get to lightning!