Electrocution: Lightning Strikes Erode Mountains

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Boom, zap, pow! Who needs superheroes to move mountains, when lightning does the job just fine?

Add lightning to a volcanic eruption and the event seems otherworldly!
Martin Rietze with permission

Powerful explosions sparked by lightning create piles of angular, jumbled rocks atop mountain summits, a new study shows. The frequent blasts break down high peaks more quickly than frost-shattering — when freezing water wedges apart fractured rock.

Time to Eat, Zap, or Neuter Invasive Species

In Lesotho's Drakensberg mountains, a single lightning bolt can blow out 100 to 350 cubic feet (3 to 10 cubic meters) of bedrock, said Jasper Knight, lead study author and a geomorphologist at Wits University in South Africa. The sheer volume of summer lightning strikes atop high peaks, combined with their massive erosive power, means electric blasts are a long-overlooked force in bringing down mountains, Knight and his co-author conclude.

"Lightning is very significant in causing landscape erosion and the formation of lots of fractured bedrock," Knight told LiveScience's OurAmazingPlanet. "What I think this project does, in highlighting the role of lightning, is go some way toward overturning a very entrenched and long-held paradigm of how many continental scale landscapes have evolved." (Electric Earth: Stunning Images of Lightning)

Dynamic force

Bare peaks above 10,000 feet (3,050 meters) tend to fall down very, very slowly, over hundreds of thousands of years, or so the thinking goes. The leisurely breakdown takes place primarily by water melting and freezing inside cracks, which breaks rocks into pieces. Examples of mountains eroding this way in the United States include the Wind River Range, the Sierra Nevada and the Rocky Mountains.

"Often people studying these regions have assumed they are just sitting there, they're not changing very much," Knight said. "Our study shows that we can have quite dramatic changes over the time scale of a single lightning strike. These mountains are far more dynamic, and changing far more quickly, than we realized."

While the study is the first to quantify lightning-caused erosion, geologists have traded stories of rocks hit by lightning strikes for nearly a century, Knight said. The evidence is anecdotal but obvious: Lichen seared off rocks, freshly fractured surfaces, boulders blown out of place and, in some cases, the fierce heat creates a thin, melted crust called fulgurite.