Lightning Strikes Cause Rocks to Explode: Mountains in Africa Not So Stable

Mountains may seem stable and unchangeable. With their immovable rock faces and sturdy structures, these formations seem like a fixed part of the landscape. Now, scientists have discovered that lightning strikes may cause rocks to explode and may play a huge role in shaping these mountain landscapes; in fact, it turns out that mountains may be a lot less stable than we thought.

Previously, angular debris on mountain landscapes in southern Africa were thought to have been created by changes typical of cold, periglacial environments. For example, they could have been formed due to fracturing due to frost; water enters cracks in rocks and when it freezes, it expands and causes the rocks to split apart.

Yet it turns out that this might not be how the mountains were shaped. In order to examine what might be the cause, the researchers turned to compasses.

"The energy of the lightning hitting the land's surface can, for a short time, partially melt the rock and when the rock cools down again, it takes on the magnetic imprint of today's magnetic field, not the magnetic field of millions of years ago when the rock was originally formed," said Jasper Knight, one of the researchers, in a news release.

In fact, if you pass a compass over an area where a lightning strike occurred, the needle will suddenly swing 360 degrees. Knowing this, the researchers mapped the distribution of lightning strikes in the Drakensburg.  They found that lightning significantly controls the evolution of the mountain landscapes; it shapes summit areas, which are the highest areas, with this blasting effect.

The findings are important for better understanding how this region could be impacted in the future. The stability of the land's surface has important implications for the people living in the valleys below the mountain. In addition, the mountains are inextricably linked to food security and water supply. In Lesotho, a country critical to South Africa's water supply, food shortages are leading to overgrazing, which expose the rock surface and make mountain landscapes even more vulnerable to weathering by lightning and other processes. Understanding how these mountains are shaped is crucial for planning for the future.

The findings are published in the journal Geomorphology.