Lightning Strikes Shape Mountains

By: By Laura Dattaro

Published: October 21,2013

 

 

 

 

New research shows that lightning strikes play a large role in the shaping of mountains. (Pascal Pochard-Casabianca/AFP/Getty Images)

When Jasper Knight and Stefan Grab used a compass to explore the mighty Drakensberg mountain range, they needed it to guide them not through space, but through time.
Knight and Grab, both geoscientists at Wits University in Johannesburg, held their compass out over the rocks of the Drakensberg, the highest mountain range in southern Africa, looking for evidence of lightning strikes. What they found leads them to believe that lightning and other climatic factors play a much greater role in the shaping of mountains than previously thought.
“The viewpoint has been that these mountains are passive agents, that their presence today and their physical properties today bear no relation to today’s climate,” Knight told Weather.com. “But what we’ve been able to show is that this is not the case at all. These landscapes are changing much more quickly than we had previously realized.”
Basalt rocks, like the ones Knight and Grab are studying, form from molten material that cools into a solid mass. Any magnetic material inside the rocks coalesces in alignment with magnetic north, leaving a signature of the rock’s physical relation to north. Since the continents have shifted since the rocks of the Drakensberg first cooled 180 million years ago, rocks that might form today would bear a different magnetic signature than the rocks that formed then.
Lightning strikes, it turns out, deposit so much energy in such a short period of time that the rocks undergo partial melting. When they cool again, their magnetic material relines up with north, giving parts of the rock a new magnetic signature — causing a compass to spin rapidly 360 degrees.
The widely accepted view has been that angular formations like the one Knight and Grab are studying were formed over hundreds of thousands or even millions of years, as water seeped into tiny cracks in the rocks and then, upon freezing, expanded and cracked them open further. This new evidence shows that mountains, generally viewed as passive and unchanging, are actually dynamic, reactive systems.
The research can be extrapolated to mountains all over the world, Knight said, meaning that our landscapes are much more susceptible to climate than we previously thought. The researchers are next looking at how the lightning strikes create debris, which can flow down into rivers or create landslides, both of which are a concern for communities that live and farm near mountains.
“The bigger connection here is that this process of generating loose debris on mountain sides is part of a much bigger picture of soil erosion,” Knight said. “These mountainous landscapes are becoming unstable as a consequence of over grazing. Very high rates of soil erosion are exposing new bare surfaces. This is helping to destabilize the whole of these mountain landscapes.”
The research will be published in a paper in the journal Geomorphology.
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Photo courtesy Martin Rietze.