Fulgurites: Petrified Lightning in the Ground
A Busy Day for Thunderstorms and Lightning
Lighting strikes the Earth at least a hundred of times every second!
According to the U.S. Dept. of Energy, there are over 16 million lighting storms annually with at least 2000 lightning storms happening somewhere in the world right now. There are at least 100 lightning strikes hitting Earth every second...
These figures are surprising, but equally surprising are something rare and wonderful that happens when lightning strikes sandy, quartz or silica-laden ground; the creation of Fulgurites!
Under certain conditions when lightning strike the ground, it will melt the soil and quartz-like sand or silica, creating slender hollow glass-like tubes called fulgurites. If this occurs on a grassy field or yard, often the grass is incinerated making it easy to locate the strike. It is pretty easy to tell a lightning strike because of the dead grass and disrupted earth. The soil on or just under the surface often has melted, the quartz and silica have fused into masses or fulgurite tubes.
Quartz is the second most abundant material on Earth after feldspar. Typically, a lightning strike on a sandy beach or on soil with an underpinning of sand with quartz can reliably produces fulgurite.
A Lightning Strike Fulgurite (image source)
The process of lightning creating fulgurites is very fast, taking approximately one second. Heated to temperatures of around 3,2700 F (1,8000 C) the soil and clay melts into a silica following the winding path of the lightning. What is created is a glass tube in-situ in the shape of the path the lightning took. This hard glassy material is sometimes also called "petrified lightning."
Fulgurites can be small, the size of a pencil eraser or smaller or then can be several centimeters in diameters and their root-like structure run as much as 49-feet or more. Often sought by collectors and mineralogists for their rarity, these fulgurites sometimes are available in gem and crystal shops, other retail shops and the very large one can be in museums. Generally black or tan, colors can occur depending upon what type of sand this occurs in.
This melted mineraloid, also called "lechatelierite" which is a substance that does not demonstrate orderly crystallinity, can also be created under other conditions such as a meteorite strike, volcanic explosion and even a when high-voltage utility line discharges into the ground. If the soil conditions are right for fulgurite creation, the high-power line will produce a 'melted slag' from the local soil minerals present.
In the early spring of 2009 just down the street from us, just such an event occurred. An overhead high-voltage line fell to the sidewalk during a violent thunder & lightning storm where it arced and scorched the sidewalk and part of a residential yard. A length of this live power line laid across a section of a grassy yard near the sidewalk and a string of man-made fulgurites about 25 feet long were created! (See images below-left.)
They are not much too look at; even the best fulgurites are rather unattractive. The ones produced by lightning are often tubular and hollow. These ones I examined here did not appear to have any hollowness to them. They are definitely brittle; one can break them apart with relative ease. They are 'petrified lightning' and even today, nearly one year later, these fulgurites in the image are still embedded in this yard. I should gather some for a more in-depth examination.
A quick check on the internet reveals that there are collectors and retailers of lightning-produced fulgurites. I would even suppose that there are hardy individuals that might even concoct ways to induce lightning to strike beaches and create new fulgurites, whereby they come back later and dig-up these petrified lightning strikes.
Lightning is Beneficial for Life
Lightning in the air creates ozone which helps shield us from solar radiation. And lightning binds the gas nitrogen to water droplets which fall to the Earth as rain, along with ozone which combines with water vapor to create naturally-occurring hydrogen peroxide. Plants cannot absorb nitrogen through their leaves of course, but they uptake nitrogen through the roots. This is a natural nitrogen fertilizer that lightning has provided, dissolved in the rain. The minute amounts of hydrogen peroxide that makes it to the surface soaks into the soil where the additional oxygen makes plants grow better, -just another factor why rainwater is better for your plants.
There is even radical thinking that lightning strikes that penetrate deeply into the ground may actually create seed crystals, forming the basis that larger crystals 'grow' from. Furthermore, a lightning strike may 'open up' cracks deep in the ground through which water can flow and erode, and this in turn creates subterranean caves. Even more radical a theory is that stalactites (those hollow tubes of minerals that hang from many cave ceilings) may have in fact started as fulgurites and thereafter, have had mineral deposits encase them! Stalactites may have been formed by lightning strikes! This theory has yet to be confirmed, but often in caves with stalactites there is also evidence of lightning strikes! So perhaps those crystals that allegedly took hundreds of thousands of years to grow in fact grew very rapidly initially and with the help of lightning strikes!
While the adage 'lightning never strikes the same place twice' has been roundly rejected and disproved time and time again, it is noteworthy to point out once again that yes, lightning DOES indeed strike the same place repeatedly. Straw, stick and thatch villages in Africa for instance that have stood on the same ground for generations of families and employ the use of a campfire within the living quarters has been shown to increase the likelihood of a lightning strike. It is the carbon black from the burning of campfire wood that is responsible. These deposits of carbon layer into the ground and are slightly more conductive than the surrounding soil. Thus, slightly more likely to attract a lightning strike. Villagers are encouraged to move their home's location every few years to avoid these inadvertent concentrations of carbon build-up.
Corning Museum of Glass (Corning, NY) Fulgurite Collection
Lightning strikes seem to be commoner these days. DISCOVER magazine (April 2010, p.16) mentions a study by NASA and Hebrew University of Jerusalem that air pollution and carbon from automobile exhaust are increasing lightning strikes by as much as 25%. It appears that the the extra particulates in the air create pathways for lightning to form, much like the lightning bolts seen in the clouds of exploding volcanoes.
Some Gathered Fulgurites from the Downed Power Line Incident
(images by author except where given attribution)