Glass Lightning
Let's start with an interesting fact: A typical cloud-to-ground lightning bolt is hot. Very hot. The air surrounding a lightning stroke is superheated plasma, which can be anywhere between 30,000 and 50,000 degrees Fahrenheit. By way of comparison, the outer layer of the sun is around 11,000 degrees Fahrenheit.
Worldwide, there are about six thousand lightning flashes per minute. Not all these flashes are cloud-to-ground strokes, but even so, that's a lot of lightning strikes every minute.
Some of these lightning bolts hit sand. Sand is primarily silicon dioxide, SiO2. When sand is heated above about 900 degrees Fahrenheit or so, it melts and fuses into an amorphous solid that you're probably familiar with; in this form, it's called "glass."
When lightning meets sand, all the energy in the lightning bolt spreads out, melting it into glass as it goes. The result is a formation called a "fulgurite," a brittle glass tube that traces the pattern of the lightning in the sand.
Fulgurites are typically hollow tubes, and may be anywhere from a few inches to several yards long. The length and width are proportional to the strength of the lightning bolt, and also depend on the characteristics of the surface where the bolt hit. The heat of the lightning bolt rapidly melts the sand, which cools just as quickly to a solid tube that preserves the path the lightning took through the ground. The tube is usually very fragile, partly because the sand is rarely pure (inclusions in the glass weaken it) and partly because it cools much too rapidly to anneal, so thermal stress is locked into the glass.
Fulgurites can spread for a great distance underground, depending on the composition of the material beneath the point of impact. Large fulgurites are uncommon, mostly because people who dig them up tend not to be careful with them; you can find fulgurites by digging at almost any beach, but it takes great skill and delicacy to dig up a large fulgurite without destroying it. This Web page shows the process of discovering and unearthing an enormous fulgurite in Seven Springs, Arizona.
Occasionally, lightning will strike an outcropping of rock (or other hard material like concrete). When this happens, the lightning will melt a channel through the rock, creating a "rock fulgurite". Rock fulgurites are a part of the surrounding material, and trace the exact path the lightning took as it passed through the material. The heat of the lightning is sufficient to change the material as the bolt passes through it, leaving a kind of "fossil" behind. (Click this thumbnail for a bigger image.)
Fulgurites can be created artificially as well. Two techniques are used for doing this. One is to attach a lightning rod to a metal stake in the ground by a thick cable, and then wait for lightning to strike; when lightning hits the rod, the energy is conducted into the cable, and a fulgurite forms where the stake is driven into the ground.
The second (and more dramatic) way to create fulgurites is to use small rockets to trigger lightning, like we talk about here.
Images: University of Florida
I live in Seaside, OR and of course I am just a block away from the beach. I am very interested in Fulgurites and am wondering what I would need to look for in order to find one on the beach? Seaside doesn't get very much lightning, I'm not sure why, but I know that at least twice a year we do get lightning strikes and this year we did have a Large thunderstorm which produced lightning. What should I be looking for when walking on the beach?
If lightning strikes a sandy beach, it melts the sand into glass, forming a tube of melted sand outside the lightning channel and vaporizing the sand from inside the tube.
After cooling, these glass-like hollow tubes can sometimes be located beneath the surface of the sand. The outer surfaces are often rough with adhering un-fused quartz sand grains. The inner surfaces and opening of the tube are usually smooth and glassy.
Im very interested in this topic, and would like to use it for a chemistry research project. Could you give me any more information or sites relating Fulgurites to chemistry.