A tanker drives near a chasm suspected to have been caused by a heavy downpour along an underground fault-line near the Rift Valley town of Mai-Mahiu, Kenya. Picture: Thomas Mukoya/Reuters

Mai Mahiu - Eliud Njoroge and his wife were inside their house in Kenya's Rift Valley when a crack appeared in the cement floor and started spreading.

As they raced out they already knew it was more than a construction fault. Other cracks had already started to appear on their town's main road- a major thoroughfare to the Maasai Mara nature reserve - after weeks of rain, floods and tremors.

In the days that followed, geologists started to take full stock of the disaster - a giant fissure, kilometres long, slicing through the road and surrounding countryside - a harsh reminder that Kenya's majestic Rift Valley, a tourist hotspot, sits on some of the most unstable ground on the continent.

"My wife screamed for the neighbours to come and help us remove our belongings," Njoroge said, remembering when they first noticed the crack in their home in the town of Mai Mahiu on March 18.

In the days that followed, the house became so unstable it had to be demolished. Njoroge was left searching for salvage in the piled up bricks and corrugated tin sheets. The couple are still looking for a place to stay.

The road was fixed in a day. But the fissure has forced other families to leave and geologists have warned it could spread further with more heavy rains expected over the next two months.

"People on the ground should be sensitive especially when it rains. Checking whether there are cracks, ground that is sinking or tremors," said geologist David Adede.

"The cracks run almost in a straight line so you can project. If you see a crack coming your way, get away,” he added.

In the very long term - over the next tens of millions of years - geologists say the underlying tectonic fault could split the continent in two.

In the meantime, geologists have warned that authorities need to do more to take fault lines into account as they plan their new roads, rail lines and infrastructure projects.

"They constructed the road without knowing there was a fault line, that's why the contractors are on standby since they don’t know where the crack is going," said Adede.