When rifted lakes dry up they can cause earthquakes and explosions

An aerial view of the crater seen south of Lake Turkana, Kenya

Martin Harvey/Alamy

The dry climate of East Africa has reduced the amount of water in Kenya's Lake Turkana over thousands of years, unleashing earthquakes and volcanoes from beneath it. This climate change threat could eventually affect other bodies of water around the world as rainfall and drought patterns change.

Lake Turkana is often called the cradle of humanity, as fossils up to 4.2 million years old have been found there of at least six hominin species, some of which appear to have coexisted. As the lake has shrunk over recent millennia, human ancestors have had to contend not only with a dry climate, but also with greater seismic activity.

“We hypothesize that there would have been more frequent earthquakes and more frequent volcanic eruptions during these time periods,” says Christopher Schultz, of Syracuse University in New York. “This would have exacerbated the already difficult conditions that can be observed today in that area.”

Lake Turkana is located between Kenya and Ethiopia in the Great Rift Valley, a place where the continental plate slowly divides and spreads. It's the world's largest desert lake, a body of green saltwater surrounded by sandy scrub and stormy outcrops. But nine thousand years ago, the lake was larger and surrounded by lush grassland and pockets of forest.

Between 4,000 and 6,000 years ago, the climate became drier and the water level in the lake dropped by 100 to 150 metres. Lower water levels create less pressure on the lake bed below, which can affect seismic activity. To determine the effects of this climate change, Schulz and his colleagues identified specific sedimentary layers that correspond to different time periods in subsurface samples previously taken from the lake floor.

From a boat, they conducted sonar imaging at 27 faults on the lake floor to see how much the layers of sediment were dislodging themselves from each other vertically on either side of each fault. They found that as the climate dried out, the sides of the faults began to slide past each other more quickly, increasing at an average rate of 0.17 mm per year.

“The main process is literally kind of pinning or loosening this zone of deformation, which is the zone of slip that leads to earthquakes,” Schulz says. “The drier system and lower load of the lake allow it to slide more easily.”

Computer modeling suggests that the reduced water mass also allows more magma to flow from the bottom of the lake. One of the three volcanic islands in Lake Turkana erupted in 1888.

Scientists have previously found that lower sea levels led to increased volcanic activity at ocean ridges. But this is the first clear evidence of this happening around the lake, says Ken McDonald of the University of California, Santa Barbara. “It's almost like popping the cork on a champagne bottle,” he says. “As you reduce this pressure, the more likely the magma in the crust is to rise and explode.”

While increased rainfall due to climate change is now raising water levels in Lake Turkana again, it will take thousands of years for earthquakes and volcanoes to be significantly suppressed.

But seismic risk assessments must begin to consider how a changing climate will affect water levels, according to the study authors. Governments should take earthquake risks into account before they build or remove dams.

“They should put [seismometers] “Before making any huge changes,” MacDonald says.

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