Mai Mahiu-Narok road, in a region just west of Nairobi, Kenya, used to be fully intact.

Then, after a period of heavy rainfall late last month, a massive crack was exposed. According to the local news outlet, Daily Nation, it measures 50 feet deep and 65 feet wide in some spots.



Geologist David Adede, who spoke with the paper, said the crack was likely filled previously with volcanic ash from nearby Mt. Longonot. This means the space was only exposed when rainwater washed the ash away.



Reuters reports that the opening formed rapidly. One resident named Eliud Njoroge Mbugua saw the crack run through his home. He was only narrowly able to collect some of his belongings before his house collapsed.



So what caused the break in the first place?

Great Rift

The crack, only recently exposed from its hiding place in the Earth, is part of the Great Rift Valley.

The name is often used to refer to a cultural region from the Middle East to Mozambique, but is not actually connected to the same unit. Rather it's made of multiple rifts all running through the same system.



(Read more about the social rifts felt in this region.)



A rift valley refers to a lowland region where tectonic plates rift, or move apart. The large crack that recently exposed itself in Kenya is from the East African Rift. In the 3,700 mile-long East African Rift, there are two smaller systems called the Gregory Rift and the Western Rift, and each is speckled with volcanoes.



The rifts are growing larger as two tectonic plates, the Somali plate in the east and the Nubian plate in the west, move away from each other.

The region has yielded some of history's most important archaeological finds and has been nicknamed the “cradle of humanity.” “Turkana boy,” a 1.5-million-year-old hominin skeleton was found there. It's an important piece of evidence for scientists piecing together our prehistoric past.



While it's one of the largest, the East African Rift isn't the only geological formation of its kind. Eastern Russia is home to the Baikal Rift Valley, and Antarctica is separated by the West Antarctic Rift.



In the U.S., the southwest is sliced by the Rio Grande Rift Valley, which stretches from Chihuahua, Mexico to Colorado. It's formation, roughly 30 million years ago, is responsible for the Rio Grande River bordering the southern U.S.



A Growing Divide

Eventually, the Somali plate may completely separate from the Nubian plate and form a separate land mass comparable to Madagascar or New Zealand. Fortunately for those who live there, that separation isn't expected to happen for another 50 million years. It does mean, however, that the physical effects of that separation will continue to be felt.

The Daily Nation reported that transportation officials often blame the rift for infrastructure issues, and it's not known how safe a new railway in the region is.

Local outlet NTV reported that in the days since the rift occurred, the crack has been filled in with a mix of concrete and rocks and is being used as a road once again.