Scientists believe carbon dioxide release into the atmosphere from Earth’s interior takes place mostly via degassing from active volcanoes, but carbon dioxide can also escape along faults away from active volcanic centers.

Scientists believe carbon dioxide (CO₂) release into the atmosphere from Earth’s interior takes place mostly via degassing from active volcanoes. CO₂ can also escape along faults away from active volcanic centers. However, such tectonic degassing was poorly constrained, and to date has been largely unmeasured. DCO’s Tobias Fischer (University of New Mexico, USA) and colleagues conducted research to effectively study carbon emissions through fault systems in the East African Rift (EAR) in an effort to understand carbon emissions from Earth’s interior and how it affects the atmosphere. Their work was published in Nature Geoscience, and was part of a continued effort to better quantify global emissions of CO₂ from Earth’s interior [1].

These new measurements contribute to improving their understanding of how carbon moves from the mantle to the atmosphere, a main focus of DCO’s Deep Carbon Degassing (DECADE) effort. DECADE was an initiative within DCO to instrument currently active volcanoes for continuous CO₂ flux measurements, and also to better quantify CO₂ emissions from volcanic and active tectonic regions that have not yet been measured. DECADE recently supported expeditions to the Aleutians and South America to constrain volcanic carbon emissions. The East Africa work shows that continental rifts were major, previously largely unquantified, contributors to global carbon flux.

Led by UNM Ph.D. student Hyunwoo Lee, the lead author of the paper, the scientists set out to measure diffuse CO₂ flux from the Magadi-Natron basin in the East African Rift (EAR) between Kenya and Tanzania.

“CO₂ was the main source of the greenhouse effect,” said Lee. “Natural carbon emissions come from volcanoes and are derived from magma. Mostly, people have thought the major sources of magmatic emissions have come through active volcanic events. Their research was the first attempt to quantify magmatic CO₂ gases from non-volcanic and continental rift regions.”

The EAR was the world’s largest active continental rift and was comprised through distinct western and eastern sectors. Several active volcanoes emit large volumes of CO₂ including Nyiragongo in the Congo and Oldoinyo Lengai in Tanzania. Additionally, significant amounts of CO₂ were stored in large anoxic lakes in this region.

Additional gas samples collected along fault zones in the Magadi-Natron basin showed elevated CO₂ flux and provided further evidence that faults act as permeable pathways facilitating the ascent of deeply-derived CO₂. This particular study area represented a conservative 10 percent of the entire Natron-Magadi region. The team then compared the data to gas data from the active volcano Oldoinyo Lengai, and found carbon isotope compositions indicating a strong magmatic contribution to the observed CO₂ degassing.

“We found that about 4 megatonnes per year of mantle-derived CO₂  was released in the Magadi-Natron Basin, at the border between Kenya and Tanzania,” Lee said. “Seismicity at depths of 15 to 30 kilometers detected during our project implies that extensional faults in this region may penetrate the lower crust.” Thus, the ultimate source of the CO₂ was the lower crust or the mantle, consistent with the carbon isotopes measured in the gas.

The findings suggest that CO₂ was transferred from upper mantle or lower crustal magma bodies along these deep faults. Extrapolation of the measurements to the entire Eastern branch of the rift system implies a huge CO₂ flux of 71 megatonnes per year, comparable to emissions from the entire global mid-ocean ridge system of 53 to 97 megatonnes per year.

“It is often argued that large volcanic eruptions instantly transfer significant amounts of CO₂ and other gases into the atmosphere where they affect the global climate over a few years,” Fischer said. “On human time-scales, continental rifting is extremely slow at spreading rates of mm’s per year but on geologic time-scales, rifting can be considered a catastrophic continental break-up event.”

Large-scale rifting events could play a previously unrecognized role in heating up the atmosphere and perhaps ending global ice ages.

Cindy Ebinger, a professor of earth and environmental sciences at the University of Rochester, USA, coordinated field activities near the Kenya-Tanzania border and analyzed earthquake patterns within the rift zone.

“The unique coupling of gas chemistry and earthquake studies made it possible to discover the escape of gas along permeable fault zones that serve as conduits to the surface,” said Ebinger. “The work also allowed us to document the process of crustal growth through the formation of igneous rocks from magma in early-stage continental rift zones.”

Lee says the scientists plan to measure diffuse CO₂ flux and collect gas samples from other areas in the EAR to better constrain how much it releases deep carbon to try to better constrain how much deeply derived CO₂ comes from natural systems.

“Because some geological settings, for example fault zones, have never been paid attention to, global CO₂ flux from natural systems are obviously underestimated,” he said. “Although there are still many ongoing studies to find better ways to quantify CO₂ flux from active volcanoes, we expect this study to trigger more research on CO₂ output from non-volcanic areas.”

Additional scientists involved in the study included: James Muirhead (University of Idaho, USA), Zach Sharp (University of New Mexico, USA), Simon Kattenhorn (University of Idaho, USA), and Gladys Kianji (University of Nairobi, Kenya.

The volcanic island of Ambrym, located in the archipelago of Vanuatu in the South Pacific, was one of the most active volcanoes on Earth. What makes it particularly significant was its role as a major emitter of deep carbon dioxide (CO₂) and other magma-derived gases. Ambrym ranks among the top three volcanic emitters worldwide, highlighting its contribution to the global carbon cycle. The release of these gases plays a critical role in understanding volcanic processes and the movement of carbon between the Earth’s interior and atmosphere.

The Geological Setting of Ambrym

Ambrym was part of the Vanuatu volcanic arc, formed by the subduction of the Indo-Australian plate beneath the Pacific plate. The island was home to two persistent lava lakes—Benbow and Marum—which contribute to its continuous emission of volcanic gases. The volcano’s magma chamber connects deep within the Earth’s mantle, making Ambrym a key player in the deep carbon cycle by releasing CO₂ that has been stored for millions of years.

 

Volcanic Emissions from Ambrym

Ambrym emits an enormous volume of volcanic gases, primarily composed of:

• Carbon Dioxide (CO₂)
• Sulfur Dioxide (SO₂)
• Water Vapor (H₂O)
• Hydrogen Chloride (HCl)

These gases were released through eruptions, degassing from lava lakes, and fumaroles, with CO₂ being the most significant in terms of its impact on the carbon cycle.

Key Role of Deep Carbon Dioxide (CO₂)

• Ambrym’s CO₂ emissions were directly sourced from magma deep in the mantle, making it one of the world’s most prominent volcanic contributors to the global deep carbon cycle.
• It releases approximately 10,000–30,000 metric tons of CO₂ per day, rivaling other major volcanic emitters such as Mount Etna (Italy) and Kīlauea (Hawaii).
• These emissions provide critical insights into how carbon stored in the Earth’s mantle was transferred to the atmosphere.

 

Impact on the Global Carbon Cycle

Ambrym’s emissions represent an essential component of the decade-deep carbon cycle, which regulates Earth’s climate over geological timescales. While most atmospheric CO₂ comes from human activities, volcanic sources like Ambrym release ancient carbon that has been sequestered deep within the Earth. The study of these emissions helps scientists better understand:

• Long-term climate stability: How volcanic CO₂ contributes to Earth’s natural carbon balance.
• Volcanic climate feedbacks: The impact of large-scale eruptions on atmospheric CO₂ levels and global warming.
• The mantle’s carbon budget: How much carbon was stored, transferred, and released from deep within the Earth.

 

Volcanic Activity and Degassing at Ambrym

Ambrym’s continuous lava lake activity drives its exceptional gas output. Unlike explosive eruptions, which release gases in sudden bursts, Ambrym’s lava lakes emit gases steadily over time, contributing to sustained high levels of CO₂ and other volatiles. This consistent degassing makes Ambrym a crucial site for monitoring volcanic carbon emissions.

 

Monitoring and Scientific Research

Given its significance, volcanologists and climate scientists closely monitor Ambrym’s volcanic activity and emissions. Advanced tools such as:

• Satellite-based measurements (like NASA’s OCO-2)
• Ground-based infrared spectrometers
• Volcanic gas sampling drones

These tools allow researchers to track gas emissions in real time, helping improve volcanic hazard assessments and climate models. Understanding Ambrym’s gas output also contributes to refining predictions about the role of volcanic CO₂ in climate change.

 

Comparison with Other Major Volcanic Emitters

Ambrym stands alongside Mount Etna in Italy and Kīlauea in Hawaii as one of the top three volcanic sources of deep CO₂. Here’s a comparison:

Volcano	Location	Average Daily CO₂ Emissions	Primary Gas Source
Ambrym	Vanuatu	10,000–30,000 metric tons	Mantle magma
Mount Etna	Italy	10,000–20,000 metric tons	Mantle plume
Kīlauea	Hawaii, USA	5,000–9,000 metric tons	Basaltic magma

Ambrym’s high emissions result from its persistent lava lakes and open vent structure, making it a continuous emitter of CO₂ even during non-eruptive phases.

 

Environmental and Climate Implications

The continuous release of volcanic CO₂ from Ambrym and other active volcanoes plays a complex role in Earth’s climate. While volcanic CO₂ emissions contribute to long-term warming trends, they were relatively small compared to human-made emissions. However, volcanic activity has historically triggered climatic shifts over geological timescales, such as during periods of increased volcanic eruptions in Earth’s past.