Dry climate accelerates East Africa’s breakup

Over the past 5,000 years, East Africa has become arid. Now, new research has found that this change may be accelerating continental separation.

A study published in the journal Scientific Reports in November found that the formation of faults in the East African Rift Valley has accelerated since the water levels of the massive lake have declined.

Christopher Scholz, the study’s lead author and geologist, physicist, and professor emeritus at Columbia University, said the findings highlight the bidirectional relationship between climate and plate tectonics.

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“Usually we think of it the other way around: mountains are built and that changes the climate of a region or region,” Scholz told Live Science. “But it can also work the other way around.”

Scholz and his colleagues conducted the study in Kenya’s Lake Turkana. The lake is 155 miles (250 kilometers) long, 19 miles (30 kilometers) wide, and reaches a depth of 400 feet (120 meters) in places. But this is nothing compared to the water level more than 5,000 years ago, when the lake was up to 500 feet (150 m) deep.

This was during the African Wet Era, when many parts of Africa were wetter than they are today. In East Africa, this period lasted from about 9,600 years ago to 5,300 years ago, with drier conditions prevailing during the past 5,300 years. The researchers studied sediments on the lake bed to determine ancient water levels and sediment flows into Lake Turkana. In the process, they noticed many small faults and traces of ancient earthquakes in the sediments.

Africa’s underlying tectonic plate is pulling apart in eastern Africa, and could one day split into two plates across the ocean. The region’s deep, narrow lakes, including Lake Turkana and nearby waterways such as Lake Malawi in Tanzania and Mozambique, are the result of this rifting process, which is creating deep valleys in the region.

Scholz and his team wanted to know whether changes in the lake itself were influencing this rifting process. Water is important for tectonics. For example, when a glacier retreats, the weight of the glacier is lifted and the land beneath it actually rises up like bread rising. This is a process called isotropic repulsion. Large amounts of water can push down on the underlying crust as well, affecting processes such as earthquakes.

The researchers found that the Lake Turkana fault moved faster after the end of the African Wet Period, exhibiting an average of 0.007 inches (0.17 millimeters) of extra movement per year. In general, Africa is cracking at a rate of 0.25 inches (6.35 millimeters) per year.

Using computer simulations, the researchers determined that there are probably two causes for this earthquake acceleration. One is that there is less water squeezing the Earth’s crust, allowing faults to move more freely. Imagine you are loosening a vise around two wooden planks. The other cause is more indirect. An island on the south side of Lake Turkana is home to a volcano with an active magma chamber. Removal of water from the Wet Africa depressurizes the mantle beneath this volcano, causing further melting. That melt then moves into the volcano’s magma chamber, causing it to expand and causing further tectonic activity at nearby fault lines.

“Due to the strengthening of the faults during this period, we believe that earthquakes are more prevalent in this wider region today than they were 8,000 years ago,” Scholz said.

Researchers are currently working on a project to examine changes in water levels in Lake Malawi going back 1.4 million years, hoping to better understand how climate influences the separation of continents.

“This information about large changes in water levels in these lakes is a very important part of this story,” Scholz said.