When rift lakes dry up it can cause earthquakes and eruptions

A dry climate in East Africa reduced the amount of water in Kenya’s Lake Turkana for thousands of years, triggering earthquakes and volcanoes beneath it. This climate change risk 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 because 4.2 million-year-old fossils have been found there from at least half a dozen hominid species, some of which appear to have coexisted. As the lake shrank over the past few millennia, these human ancestors would have faced not only a drier climate, but also greater seismic activity.

“We postulate that there would have been more frequent earthquakes and volcanic eruptions during these time intervals,” says Christopher Scholz of Syracuse University in New York. “This would have worsened the already difficult conditions that can be observed today in this region. »

Lake Turkana is located between Kenya and Ethiopia, in the Great Rift Valley, a place where the continental plate is slowly splitting and expanding. It is the largest desert lake in the world, a body of greenish, salty water surrounded by sandy scrub and windy outcrops. But nine millennia ago, the lake was even larger and surrounded by lush meadows and pockets of forest.

4,000 to 6,000 years ago, the climate became drier and the lake’s water level dropped by 100 to 150 meters. Lower water levels create less pressure on the lake bed below, which can impact seismic activity. To determine the effects of this climate change, Scholz and his colleagues identified certain layers of sediment corresponding to different periods in cores previously taken from the bottom of the lake.

From a boat, they then performed sonar imaging on 27 faults in the lake bed to see the extent to which the same layers of sediment had been displaced vertically relative to each other on either side of each fault. They found that as the climate drier, the sides of the faults began to intersect more quickly, growing on average by 0.17 millimeters per year.

“The main process is literally tightening or loosening that deformation zone, the slip zone that results in earthquakes,” says Scholz. “A drier system and lower load in the lake allows it to slide more easily.”

Computer modeling suggested that the reduced water mass also allowed more magma to flow from beneath the lake. One of Lake Turkana’s three volcanic islands erupted in 1888.

Scientists had already discovered that falling sea levels increased volcanism at ocean ridges. But this is the first clear evidence that it happens around a lake, says Ken Macdonald of the University of California, Santa Barbara. “It’s almost like loosening the cork on a bottle of champagne,” he says. “As you decrease that pressure, magma is more likely to rise up into the crust and erupt.”

While increased precipitation due to climate change causes Lake Turkana’s water levels to rise again, it would take thousands of years for this to significantly suppress earthquakes and volcanoes.

But seismic risk assessments should start by considering how climate change might affect water levels, according to the study authors. And governments should take seismic risk into account before building or removing dams.

“They should put [seismometers] before making any major changes,” says Macdonald.