| 03.21.2018

The fault in CO2 emissions – Researchers analyze CO2 emissions from East African fault line

Eastern Africa is one of the most volcanically active regions of the world. However, James Muirhead, a University of Idaho geology doctoral student, and Hyunwoo Lee, a University of New Mexico Ph.D candidate, were more interested with what was going on under the ground.

That”s why Muirhead and Lee set their sights on the East African Rift (EAR).

The EAR is the world”s largest active continental rift. These usually occur where two tectonic plates come together. Lee said they focused their research in Kenya and Tanzania, as the fault stretches parallel to much of the East African coast, while they were there for three weeks last summer.
Muirhead said prior to this, no one had really investigated the role these fault systems play on a global scale and the amount of carbon dioxide (CO2);they release.

“This is different from volcanoes,” Muirhead said. “There”s no plume of smoke, they (CO2 emissions) are nearly invisible,” said Muirhead.

Though the focus usually falls on volcanoes, he said, there”s actually magma all along the rift releasing a large amount of CO2.

It sounds dramatic, but this isn”t a giant tear in the crust of the planet with a river of lava at the bottom – it”s subtler that that, he said.

“We”re looking at diffuse emissions,” Muirhead said. “Wide-spread, low concentrations of carbon dioxide coming out of the soil.”

To measure this, they used what Muirhead called a Carbon-Dioxide Accumulation Chamber. Placed on the ground over the fault, it was used to read the amount of CO2 in the atmosphere at that point, and the rate of change of CO2 in the chamber of the device. If there was no fluctuation, the scientists knew there wasn”t a leak coming out of the ground. However, if there was a leak, they would see a flux of CO2 in the device.

“Our hypothesis was that there can be CO2 coming out of the faults from deep-seated magma bodies,” Lee said.

The question then became how to prove where the CO2 samples actually originated, and Lee is using carbon isotopes to attempt to answer it.

Lee said an isotope is another form of an element with a different atomic mass, but the same chemical properties.

“I have measured the carbon isotopes of carbon dioxide from the rift, which shows that the gas came from magma deposits, and not the atmosphere,” Lee said.

The carbon emissions have an effect on more than the atmosphere. Their paper, published   in Nature Geoscience, is titled “Massive and prolonged deep carbon emissions associated with continental rifting,” which concludes on a somewhat ominous note.

“We conclude that widespread continental rifting and super-continent breakup could produce massive, long-term CO2 emissions and contribute to prolonged greenhouse conditions like those of the Cretaceous,” the paper reads.

To Muirhead, this means two main things are going on. First, he said that continental drift is partially driven by the release of CO2, and that the pressure helps break apart the crust of continental plates. Second, this continental drift is contributing to the amount of CO2 in the atmosphere.

Two of the reasons the researchers are studying these emissions is to increase the understanding of the deep carbon cycle and the influence they have on the climate humans live in.

“Basically, we”re trying to understand the sources of carbon,” Muirhead said.

Lee said the research isn”t over yet.

“We just thought about one continental rift, but there are more continental rifts to be studied, to get more numbers, more data,” Lee said. “We want to give a message to people about how much carbon-dioxide is released from rifts versus human activities.”

Muirhead said the next plan is to go back to the EAR to see how the rates of diffusion vary throughout the rift, and to coordinate that to the amount of magma accumulating below it.

Yet Muirhead said emissions produced by the EAR are minimal – compared to the emissions created by humans, at least. He said the carbon dioxide leaking out of the EAR is about 500 times less than what humans produce per year.

“Nowadays, human activities are very important. But human beings started appearing, oh, 10,000 years ago,” Lee said. “These carbon dioxide emissions from faults, continental rifting, have been happening throughout earth”s history.”

Carly Scott  can be reached at  arg-news@uidaho.edu

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