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USF Researcher Digs Down To Determine The Power Of Lightning

Oct 4, 2016

According to NASA, the United States sees about 25 million lightning strikes per year.

The state that gets the largest number of those, by far, is Florida. The area between Tampa and Orlando is even called “Lightning Alley” because it receives as many as 50 strikes per square mile a year.

But when it comes to determining how powerful a strike is – how much energy is in lightning – the science is a little more inexact. Atmospheric physicists get a number by looking at the electrical current and temperature of bolts as they happen, but that’s an approximation.

Now, a University of South Florida researcher is helping us understand this intimidating and potentially dangerous part of living in “Lightning Alley” – and he’s using geology, of all things, to do so.

According to Dr. Matthew Pasek, an associate professor in the School of Geosciences, the process starts when a bolt of lightning hits ground made up of sand – making Florida an ideal place to conduct this research.

"The electricity hits that sand and heats it up really, really hot – we’re talking 50,000 degrees Fahrenheit," Pasek said. "It completely vaporizes the rock, and melts another portion of the rock, and that happens very fast and then it sits there and cools down, forming a glass. And the glass that gets left over is called a fulgurite."

USF Geosciences Associate Professor Matthew Pasek holds a fulgurite sample.
Credit WUSF TV

Derived from "fulgur," the Latin word for lightning, fulgurites were first discovered by scientists in the early 18th century.

"They weren’t really certain what they were for about a hundred years or so," Pasek said. "And then due to a couple, very clear lightning-fulgurite connections, they said ‘Well these are being formed by lightning.’"

Among the earliest scientists to take a closer look at fulgurites was Charles Darwin, who wrote about them in his journals.

"He did so on his voyage on the Beagle, back in the 1820’s and happened to be able to recognize them from South America, as they had a layover along the coast, and happened to find several of these in a sand plain," Pasek said. 

Close-up of a fulgurite, created when lightning super heats sand.
Credit WUSF TV

Almost two centuries later, Pasek and a colleague, Marc Hurst from Independent Geological Services, are using fulgurites in a way Darwin never imagined.

The pair have collected more than 250 samples from sand mines in Polk County. What makes those samples unusual is that they come from across time – some that they believe are thousands of year old.

No matter the age, Pasek and Hurst were able to determine how much energy was in a strike by looking at the length and thickness of the fulgurite.

"And so you can imagine that a bigger fulgurite means that there’s more energy that got put into the sand, a smaller one means that there was less," Pasek said. 

He added that lightning strikes Earth about 45 times per second, and since about a quarter of the strikes are cloud-to-ground lightning, that means as many as 10 fulgurites could be created every second.

"We still don’t exactly know why lightning strikes and so this may not help too much with understanding that, but it does give us another idea of how much energy and maybe power a lightning strike might have," he said. 

And when you look at the power of an average strike, it shows that people should really respect the power of lightning and head for shelter when a storm rolls in.

"The amount of energy is about being hit by a car going 60 miles per hour, and so that’s a lot of energy to get from a lightning strike, and it would not be something you want to have happen either end: getting hit by a car or getting struck by lightning," Pasek said. "You can survive both, but it will certainly impact your quality of life."

Pasek and Hurst’s research was recently published in the journal, Scientific Reports