It’s easy to forget that the earth beneath our feet is constantly moving – that the continents we stand on are little more than thin tectonic plates floating and jostling atop a churning sphere of hot rock.
Over geological timescales of millions of years, these tectonic plates grind past one another, wrench apart, and undergo extreme slow-motion collisions that warp and buckle their edges, erect mountain ranges and widen oceans.
These processes are usually imperceptibly slow, with movement on the order of just a few centimetres per year – or about as fast as your toenails grow. But occasionally something happens to remind us of the planet’s restless interior.
A huge crack has opened in Kenya
The world witnessed dramatic evidence of this back in March 2018, when an enormous crack opened in the ground in southwestern Kenya. The tear, which appeared suddenly after heavy rains, measured several kilometres in length and swallowed a section of the Nairobi-Narok highway.
The location of the crack, within the Kenyan Rift Valley, reignited a decades-old debate about whether Africa will one day break apart. The Valley is part of a region called the East African Rift, one of the most tectonically active regions in the world.
The rift, which began developing about 25 million years ago, extends over a staggering 3,500km (2,174 miles), from the Red Sea in the north all the way to Mozambique in the southeast of the African continent. Seismic and volcanic activity occurs along its entire length, and is responsible for creating mountains including Kilimanjaro and Mount Kenya.
Will Africa sit on two tectonic plates?
In the past, scientists thought that Africa sat upon a single tectonic plate. But since the 1970s, evidence has been mounting that the African plate is rupturing into two new plates – dubbed the Nubian and Somali plates – along the East African Rift.
Geologists and geophysicists are still debating what might be causing this to happen. The current leading theory is that plumes of heat within Earth’s mantle are making the lithosphere (the crust and solid upper mantle) beneath Kenya and Ethiopia dome and stretch.
The thinning lithosphere has generated huge volcanic eruptions called flood basalts – which send lava gushing from emerging fissures like flood waters – and fractured the brittle continental crust into a series of faults. From above, these faults, which together make up the greater Rift Valley, look like deep crevices and elongated basins separated by regions of higher land.
How fast is Africa splitting?
GPS measurements show that across the East African Rift, the Nubian and Somali plates are diverging at an average rate of 7mm (0.2in) per year, slowly pulling the continent apart. Today, the rift remains above sea level, but as it widens, the land within the valley will sink.
Eventually, oceanic waters could flood in, separating the entire Horn of Africa from the mainland. The jury’s still out on whether this will happen, but if it did it would take tens of millions of years. The Red Sea and the Gulf of Aden are examples of similar rifts at more advanced stages of evolution.
As for the crack that alarmed the world in 2018 – the consensus among geologists today is that it was a pre-existing crevice that had lain undetected because it was packed with volcanic ash from eruptions in the distant past. It was suddenly exposed during heavy rains when the deep layers of waterlogged ash collapsed. Panic over – for now, at least.
Read more:
- Does continental drift affect the climate?
- How do we know the geology of the British isles?
- How many continents are there in the world? It depends who you ask
- Scientists don’t actually have a clue how the Himalayas got so tall, study reveals
Asked by: Christian Barker, via email
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