Johannesburg - The Drakensberg gets its angular points not from erosion or temperature, but from the strike of lightning bolts.
This is the finding of a study from Wits University which shows that lightning can cause rocks it strikes to explode.
This is one of the factors that shape our landscapes.
Professors Jasper Knight and Stefan Grab, from the School of Geography, Archaeology and Environmental Studies, used a compass to make the discovery.
“A compass needle always points to magnetic north. But… if the minerals in the rock (passed over) have a strong enough magnetic field, the compass will read the magnetic field of the rock, which corresponds to when it was formed,” said Knight.
If you pass a compass over an area where a lightning strike occurred, the needle will suddenly swing through 360º.
Knight and Grab mapped out the distribution of lightning strikes in the Drakensberg and discovered that lightning significantly controls the evolution of mountain landscapes because it helps to shape the summit areas – the highest areas – with this blasting effect.
Previously, angular debris was assumed to have been created by changes typical of cold, periglacial environments, such as fracturing due to frost.
Water enters cracks in rocks, and when it freezes, it expands, causing the rocks to split apart.
This new research suggests that African mountain landscapes sometimes evolve very quickly and dramatically over short periods of time.
Knight said the new information was useful because the stability of the land’s surface had important implications for people living in the valleys below the mountain.
“If we have lots of debris being generated, it’s going to flow down the slope, and this is associated with hazards such as landslides,” said Knight.
Overgrazing also needed to be monitored as exposed rocks could be more vulnerable to lightning strikes and the resulting instability. - The Star