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Fulgurites
| Article
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12542 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
7 / 1987 |
846 Words |
| Author
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Michael Woods
Michael Woods, a contributing editor for THE WORLD & I, has
received numerous science-writing awards. |
The crackle of lightning and boom of thunder subside as the towering cumulonimbus storm clouds march toward the eastern horizon and finally vanish.
This storm is one of an estimated 1,500 to 3,000 thunderstorms in progress around the world at any given time. With lightning bolts striking the earth 50 to 100 times each second, surely the lightning leaves a calling card - a scorched patch of turf, a splintered tree limb, a zigzag pattern etched into the trunk of a tree. Perhaps even a fulgurite.
A fulgurite? What is a fulgurite?
Fulgurites are probably the least-known relic of the continual encounter between lightning and the earth. They are tube-shaped masses of glassy material that form when lightning strikes the ground and melts or vaporizes rock or soil.
Lightning packs such an enormous wallop of energy that forming a fulgurite requires only a split second. Scientists measuring the energy of lightning bolts have recorded peak currents of 200,000 amps. Such enormous surges of current can momentarily raise air temperatures to 30,000C, five times hotter than the surface of the sun.
Most fulgurites are formed when lightning strikes sandy soil and fuses it into rootlike tubules of glass. Usually fulgurites are only about an inch in diameter but may reach several yards in length.
Fulgurites have attracted the interest of scientists for almost 170 years. They were described in 1822 by the great German naturalist Alexander von Humboldt. Charles Darwin described fulgurites in his epic 1839 book, Journal of Researches into The Geology and Natural History of the Various Countries Visited by H.M.S. Beagle.
In April 1984, two boys were walking along a low ridge of land near Winans Lake in southeastern Michigan, about 12 miles north of the University of Michigan in Ann Arbor. They happened upon what appeared to be a cache of petrified dinosaur bones, with an eerie color that varied from white to light green or gray. They summoned parents, who in turn telephoned news of the find to the University Michigan's Museum of Paleontology.
Eric Essene, a petrologist, and Daniel C. Fisher, a paleontologist, came to the site. They quickly realized that the
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