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Photo of the Drakensburg Mountains with a stream in the foreground.

Lightning is one of the major forces behind shaping mountains like the Drakensburg Mountains in South Africa, scientists say.

Nigel J. Dennis, Gallo Images/Corbis

Don Boroughs

for National Geographic

Published January 5, 2014

Stefan Grab has long been familiar with the power of the lightning bolts that regularly strike the Drakensberg Mountains of southern Africa. Nineteen years ago, the geomorphologist was caught in a storm of such electric ferocity that he vowed never again to camp there in the summer.

But if you had told him at the time that lightning played a major role in shaping those mountains, he observes, "I would have said, 'You must be joking—what nonsense.'"

Not anymore. Grab and a colleague at Johannesburg's University of the Witwatersrand, geologist Jasper Knight, have just given a jolt of their own to conventional notions about the forces that shape mountains. In research published in the January 1 issue of the journal Geomorphology, they present evidence that lightning—rather than ice or heat—is the main force shattering rocks on Drakensberg summits.

Grab and Knight surveyed a quarter square mile amid Drakensberg peaks in Lesotho and found 90 sites where lightning strikes had blasted apart the basalt rock face, scattering up to ten tons of debris a dozen feet or more. The electric impacts leave behind pits up to three feet deep and can shift a boulder the size of a small truck.

The Drakensberg—like nearly all other ranges—were generally thought to have been chiseled by the weathering effects of ice, with smaller contributions from heat and naturally occurring chemicals. Turns out, "that's not the case," says Knight.

Lightning splits rock in much the same way as the better-known cause of weathering: frost shattering. Just as water expands when frozen, it also expands if it's been vaporized by lightning. This expansion occurs within cracks in the rocks, wedging blocks apart. But frost shattering generally occurs over thousands of years. Lightning, at temperatures of up to 54,000°F (almost 30,000°C), can burst rocks in milliseconds. "It basically causes a bomb to explode on the rock surface," explains Knight.

The Signs of Lightning

The fact that a lightning strike will partially melt basalt in an instant allowed Knight and Grab to develop a diagnostic "tool kit" to distinguish the sites of lightning strikes from other rock fragments. A key piece of evidence: The tremendous amount of electricity in lightning leaves a magnetic signature so strong that the needle of a compass passed over a strike site often swings wildly. And compared with other rocks in the area, lightning-blasted fragments are harder, smoother, and more often free of lichens because they are freshly broken and sheared off in an instant.

Powerful electric currents also spread tiny cracks deep within rocks. This sets the stage for water, plants, ice, and heat to weather rocks further. Lightning, says Grab, is "part of the much bigger jigsaw," a puzzle piece that had been passed over by geoscientists for decades. The impact is most obvious up close, but peaks shaped by lightning will likely look more jagged when viewed from afar, Knight notes.

The two researchers believe that further exploration will reveal other examples of mountain ranges shaped in large part by lightning—especially in warmer regions of Australia, Africa, and Asia that were mostly passed over by the Ice Age. Unlike the Rockies and Appalachians, the Drakensberg Mountains were never heavily scoured by glaciers.

No one disputes that the northern ranges were shaped largely by rivers of ice. But where glaciers have now melted and lightning storms are common, such as the southern Rockies, lightning could play an important role in the ongoing weathering of peaks. And in a warming world, that role is likely to grow.

Graphic of how lightning strikes can help form mountains.
23 comments
Tessa Skiles
Tessa Skiles

My question is why didn't anyone think of this earlier? Makes sense!

John Iley
John Iley

Lightning can fuse loose sand and evidence is preserved in fulgurites which can be found globally. Extrapolation to the erosion of rocks makes sense.

Vishnu Shriram
Vishnu Shriram

This is very interesting indeed. But how can one tell which mountains in the world have possibly been sculpted by lightning? The area would have to be one receiving a decent amount of rainfall and one where lightning storms are frequent for one. This means the requirement for a blend of warm dry regions where colder moister winds blow in. The western ghats in India ought to be decent candidates I'd say, perhaps there will be some research in the near future to shed light on this.

Jan Wiechowski
Jan Wiechowski

Man thinks he knows a lot, but really it does not know anything!

Ned G.
Ned G.

Wow! That is very interesting. I am always fascinated by electricity.

Mostafa Abd El-halim
Mostafa Abd El-halim

if As we say. The lightning and the rain and heat are reshaping the mountains. So do the mountains now are smaller than the past? And will it be in the future smaller than now?

John Warren
John Warren

This revelation is more than a proposition or hypothesis. They have done comparative analysis using magnetic field detection, surface analysis, and exploded debris field surveys to arrive at their conclusions. Their empirical data are real world and real time.

Vincent Gravenberch
Vincent Gravenberch

Let me guess. a morning someone woke up didn't got any coffee and suddenly it hits him/her. Lightning is shaping the mountains. Hahahah :)
Scientists are the number one people who are wasting money with there stupid ideas

Anthony Woods
Anthony Woods

Yikes! Or is it strikes? A 2-year and 3-year stay in South Africa and Botswana repectively allowed me to witness the terrifying power of lightening. I am thus not surprised by this proposition of its simultaneously creative and destructive role.

Z Fechten
Z Fechten

I remember seeing lightning strike a mountain in Mexico when I was a kid. I thought I saw boulders flying in the flash. No one believed me, but maybe I was right!

Vidula Deshpande
Vidula Deshpande

great. we know the force of lightening is so fierce that anything go to debris when it strikes.it is very astonishing to know that lightening plays role in shaping the mountains. nature is a great puzzle.more the man tries to solve it, more he embroils in it

Juan Rodriguez
Juan Rodriguez

This is awesome, for decades scientist had been ignored the force of lighting , the main role that plays shaping the mountains. This could help us to understand how nature is changing our geologist formations nowadays

Mostafa Abd El-halim
Mostafa Abd El-halim

Why didn't anyone before Galileo said that the earth move around the sun? Why didn't anyone before Niels Bohr explained the atomic model in that way?

I mean that everything has it's function and everyone know the function of this thing until the science discover the function of that thing

Natalie R.
Natalie R.

@Jan Wiechowski it's a tragedy of the human race that no one knows what they don't know. The less a person knows, the more convinced they are that they know everything....


That's quite an all-encompassing statement you made there, making such a claim that mankind thinks it knows a lot and then stating we know nothing....like a big 'know it all'. Just goes to show how little you do know

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