Aerial view of the crater south of Lake Turkana, Kenya.
Martin Harvey/Alami
Dry climates in East Africa have reduced the amount of water in Kenya's Lake Turkana over thousands of years, causing earthquakes and volcanic eruptions from underneath it. This climate change hazard could eventually affect other bodies of water around the world as rainfall and drought patterns change.
Lake Turkana is often called the Cradle of Humankind because fossils up to 4.2 million years old have been found there of at least half a dozen species of hominins, some of which appear to be coexisted. As the lake has shrunk over the past millennia, human ancestors had to contend not only with a dry climate, but also with greater seismic activity.
“We hypothesize that earthquakes and volcanic eruptions would have occurred more frequently during these time periods,” says Christopher Scholz at Syracuse University in New York. “This would exacerbate the already difficult conditions that can be seen in the area today.”
Lake Turkana is located between Kenya and Ethiopia in the Great Rift Valley, a place where the continental plate is slowly breaking apart and moving apart. It is the largest desert lake in the world, a body of greenish salt water surrounded by sandy scrub and winding outcrops. But nine thousand years ago the lake was even larger and surrounded by lush meadows and forests.
Between 4,000 and 6,000 years ago the climate became drier and the lake's water level dropped by 100–150 meters. Lower water levels create less pressure on the lake bed below, which can affect seismic activity. To determine the effects of this climate change, Scholz and his colleagues identified specific layers of sediment corresponding to different time periods in cores previously taken from the lake floor.
Then, from a boat, they took a sonar survey of 27 faults on the lake floor to see how far the same layers of sediment were offset 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 move away from each other faster, increasing by an average of 0.17 millimeters per year.
“The basic process is literally a kind of clamping or unclamping of this deformation zone, the slip zone, that leads to earthquakes,” Scholz says. “The drier system and less stress on the lake allows it to slide off more easily.”
Computer modeling showed that the decrease in water mass also allowed more magma to flow out from underneath the lake. One of the three volcanic islands of Lake Turkana. flared up in 1888.
Previously, scientists discovered that lowering sea levels increases volcanism at ocean ridges. But this is the first clear evidence of what is happening around the lake, says Ken McDonald at the University of California, Santa Barbara. “It’s almost like unscrewing the cork on a bottle of champagne,” he says. “When you reduce that pressure, the magma is more likely to rise up in the Earth's crust and erupt.”
Although increased rainfall due to climate change is now raising Lake Turkana's water levels again, it will take thousands of years to significantly suppress earthquakes and volcanic eruptions.
But according to the study's authors, seismic hazard assessments should begin by considering how climate change might affect water levels. Governments should consider the risk of earthquakes before building or removing dams.
“They should put [seismometers] before they make any huge changes,” MacDonald says.
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