Carbon is one of the most important elements on Earth, playing a critical role in everything from the formation of life to the regulation of the planet’s climate. While much of our focus tends to be on carbon emissions from human activities, there is another significant source of carbon that originates deep within the Earth’s mantle: carbon degassing. This natural process has profound implications for the carbon cycle, the Earth’s climate, and our understanding of geological processes. In this blog, we’ll dive deep into what carbon degassing from the Earth’s mantle is, how it works, and its implications for the environment.

What is Carbon Degassing?

Carbon degassing refers to the process by which carbon, in the form of carbon dioxide (CO2), is released from the Earth’s interior to the atmosphere. This occurs primarily through volcanic activity, where gases trapped deep within the mantle and the crust are brought to the surface during volcanic eruptions. The carbon that is degassed from the mantle has been stored for millions to billions of years, and its release is an essential part of the Earth’s natural carbon cycle.

Carbon can exist in the Earth’s mantle in various forms, including as part of minerals like carbonates or as dissolved gas in molten rock. When the conditions are right—such as during volcanic eruptions—this carbon is released into the atmosphere, contributing to the global carbon budget. The amount of carbon degassed is significant, but it is just one component of the broader process that regulates the Earth’s carbon balance.

The Mechanism of Carbon Degassing from the Mantle

The Earth’s mantle is an enormous reservoir of carbon. The carbon in the mantle is primarily stored in minerals, but it can also exist as a gas dissolved in molten rock, particularly in volcanic regions where mantle material is brought closer to the surface. When magma ascends from the mantle toward the Earth’s crust, it carries carbon along with it.

At shallower depths, the pressure decreases, causing the dissolved gases, including carbon dioxide, to come out of solution. This results in the release of carbon gases into the atmosphere during volcanic eruptions or through more passive processes like volcanic degassing at fissures and cracks in the Earth’s surface. The rate of carbon release depends on the level of volcanic activity and the specific geological conditions of the region.

In addition to volcanic eruptions, tectonic activity also plays a role in the degassing process. As tectonic plates move, they can push carbon-rich materials from the surface into the mantle, where they are stored for long periods. Over millions of years, the carbon that is sequestered deep within the Earth can eventually be released through volcanic activity.

Carbon Degassing and the Earth’s Carbon Cycle

Carbon is constantly cycling through the Earth’s atmosphere, oceans, soil, and interior. This cycle, known as the carbon cycle, regulates the planet’s climate and supports life. Carbon degassing from the Earth’s mantle is one of the key processes in this cycle, as it releases carbon that has been stored deep underground.

The carbon released from the mantle primarily comes from two sources: carbonates in the Earth’s crust and the deeper mantle material. The release of carbon from the mantle via volcanic activity and degassing represents a natural mechanism for carbon to return to the atmosphere, where it can be absorbed by plants and oceans or contribute to the greenhouse effect.

In the long run, the Earth’s ability to sequester carbon in the mantle can act as a form of climate regulation. For example, carbon stored deep in the mantle can be released gradually over millions of years, preventing a sharp rise in atmospheric carbon. However, human activities—such as burning fossil fuels and deforestation—have increased atmospheric carbon levels much more rapidly than in the past, potentially disrupting the natural balance of the carbon cycle.

Implications of Carbon Degassing for Climate Change

Understanding carbon degassing is essential for assessing its implications for climate change. While the amount of carbon degassed from the mantle is relatively small compared to human-made carbon emissions, it still plays a crucial role in the Earth’s long-term carbon budget. Over geological timescales, the release of carbon from volcanic eruptions can have significant effects on the atmosphere and the climate.

The carbon released from the mantle contributes to the greenhouse effect, which traps heat in the Earth’s atmosphere and raises global temperatures. In pre-industrial times, natural carbon degassing was balanced by the Earth’s natural processes that stored carbon, such as the burial of organic matter in sediments. However, the dramatic increase in carbon emissions from human activity has disrupted this balance, leading to an accelerated warming of the planet.

While carbon degassing is a slow process compared to human carbon emissions, it can still influence climate patterns over time. For instance, periods of increased volcanic activity—such as during tectonic shifts or the formation of large volcanic arcs—could lead to an uptick in atmospheric carbon, potentially contributing to warming trends or shifts in weather patterns. However, the natural system of carbon sequestration within the Earth’s mantle also acts to slow down the process of long-term warming, making the Earth’s carbon cycle a complex system of feedback loops.

The Future of Carbon Degassing Research

Studying carbon degassing from the Earth’s mantle is critical for understanding how our planet manages carbon over geological timescales. Geologists are increasingly using advanced techniques to study volcanic gases, including carbon isotopes, to gain insight into the behavior of carbon deep beneath the Earth’s surface. These studies help scientists better understand how carbon is stored and released over time and the long-term effects of carbon on the Earth’s atmosphere and climate.

As climate change becomes an ever-more pressing global issue, understanding the natural sources of carbon—and how they interact with human-made carbon emissions—will be essential for formulating effective climate models and mitigation strategies.

Conclusion

Carbon degassing from the Earth’s mantle is a fundamental process that shapes the planet’s carbon cycle and climate system. Though its direct contribution to current climate change is small compared to human activities, understanding this natural mechanism is key to unlocking the secrets of Earth’s long-term carbon dynamics. As research continues into the processes of carbon release and storage, we will be better equipped to predict and manage the environmental challenges posed by carbon emissions. In the broader context of climate science, knowledge of carbon degassing serves as a reminder of the intricate and interconnected systems that govern our planet’s carbon balance.

Volcanoes are more than just fiery spectacles—they play an essential role in regulating the Earth’s carbon cycle and climate. While we often think of volcanic eruptions as dramatic events that disrupt local environments, they are also a crucial part of the planet’s natural system for controlling carbon levels. These mighty forces of nature act as carbon release valves, helping to regulate the carbon stored deep within the Earth’s interior and influencing global temperatures over long periods of time. In this post, we’ll explore how volcanoes contribute to Earth’s carbon balance, their impact on climate, and their critical role in stabilizing our planet’s atmosphere.

The Role of Volcanoes in the Carbon Cycle
The Earth’s carbon cycle is a complex system involving the movement of carbon between the atmosphere, oceans, land, and the Earth’s interior. Carbon is naturally stored deep within the Earth’s mantle, and through the process of volcanic outgassing, volcanoes release carbon dioxide (CO2) into the atmosphere. This release is part of the deep carbon cycle, which operates over millions of years to maintain a balance between carbon stored in the Earth’s interior and the carbon in the atmosphere.

When tectonic plates collide and subduct beneath one another, carbon-rich materials are transported deep into the mantle. There, they can be stored for long periods, sometimes for millions of years. When the Earth’s tectonic plates shift, volcanic eruptions bring some of that carbon back to the surface in the form of CO2, where it is released into the atmosphere.

Why Volcanoes Are Essential for Climate Regulation
Volcanoes play a critical role in regulating Earth’s climate by influencing the levels of CO2 in the atmosphere. Carbon dioxide is a greenhouse gas, meaning it traps heat in the Earth’s atmosphere and contributes to the planet’s overall temperature. Volcanic eruptions release CO2, which can temporarily raise atmospheric carbon levels. However, this process is part of a long-term balance. Over millions of years, the release of carbon through volcanic eruptions has helped regulate Earth’s temperature and climate stability.

While individual eruptions may cause short-term warming, they can also have cooling effects. Large eruptions can release particulate matter such as ash and sulfur dioxide, which can reflect sunlight and cool the planet for a period. These cooling effects are often temporary, lasting from months to a few years, but they demonstrate how volcanoes are a part of the Earth’s natural climate regulation system.

The Impact of Volcanic Activity on Atmospheric CO2
Volcanic activity has long been a primary mechanism for transferring carbon from the Earth’s interior to the atmosphere. Over geological timescales, the Earth’s volcanic activity contributes to a steady release of carbon dioxide. While volcanic eruptions may seem sporadic, the cumulative effect of volcanic activity over millions of years has had a significant impact on atmospheric CO2 levels.

Interestingly, the total amount of CO2 released by volcanic eruptions is relatively small when compared to human-caused emissions from burning fossil fuels. However, the long-term, cyclical nature of volcanic carbon release plays a stabilizing role in the carbon cycle. Without volcanic eruptions, the Earth would have a much harder time maintaining the balance of carbon needed for a stable climate.

Volcanoes and the Earth’s Natural Thermostat
Volcanoes serve as a type of natural thermostat for Earth’s climate. When carbon dioxide is released into the atmosphere by volcanic eruptions, it can contribute to the greenhouse effect, warming the planet. However, this is a slow process, and over time, the Earth’s natural systems, including the deep carbon cycle, help regulate the release of carbon, ensuring that global temperatures don’t rise too quickly.

The balance between carbon storage in the Earth’s interior and the carbon released by volcanoes has helped maintain relatively stable temperatures for most of Earth’s history. Large volcanic events can cause temporary fluctuations in the climate, but over long periods, the natural cycle ensures that Earth remains habitable.

Volcanoes and Human Influence on the Carbon Cycle
While volcanic activity is a natural process that has been occurring for millions of years, human activities are now dramatically altering the carbon cycle. The burning of fossil fuels, deforestation, and industrial activities have caused a sharp increase in atmospheric CO2, overwhelming the Earth’s natural systems, including volcanic outgassing.

In recent decades, the increase in atmospheric carbon due to human activity has led to rising global temperatures and climate change. While volcanoes continue to release carbon, the amount of CO2 released by human activities far exceeds what is emitted by volcanic eruptions. Understanding the role of volcanoes in the carbon cycle is essential for recognizing the natural processes that contribute to climate regulation and the impact of human-caused emissions.

How Scientists Study Volcanoes and Carbon Emissions
Scientists study volcanic emissions to understand how much carbon dioxide is being released into the atmosphere and how it affects global carbon levels. Researchers use various methods to measure volcanic gases, including direct sampling during eruptions, satellite imaging, and analysis of volcanic rock samples. By studying volcanic activity and its impact on atmospheric CO2, scientists can better understand the long-term effects of volcanic outgassing on Earth’s climate.

In addition to monitoring current volcanic emissions, scientists also examine historical volcanic data to learn about past climate changes. By studying past eruptions and the release of carbon, scientists can gain insights into how volcanic activity has influenced global temperatures and climate stability over geological timescales.

Conclusion: Volcanoes: Nature’s Carbon Release Valves
Volcanoes are a critical component of the Earth’s natural carbon cycle, acting as nature’s carbon release valves. By releasing carbon dioxide from the Earth’s interior, volcanoes help regulate atmospheric CO2 levels and influence Earth’s climate. While individual eruptions may have short-term effects on global temperatures, the long-term impact of volcanic activity has been essential for maintaining a stable climate. Understanding how volcanoes function within the carbon cycle can help us better appreciate their role in shaping Earth’s climate and why they remain vital to the stability of our planet.

Earth is a dynamic and ever-changing planet, shaped by a variety of natural processes. While many people are familiar with surface-level phenomena like the water cycle or weather patterns, there’s a much deeper, less visible system that plays a critical role in maintaining the planet’s carbon balance. Often referred to as Earth’s “hidden engine,” the deep carbon cycle is responsible for regulating long-term carbon storage, atmospheric CO2 levels, and, ultimately, the stability of Earth’s climate. In this post, we will explore how this crucial cycle operates beneath our feet and why it matters so much to the health of our planet.

The Key Processes of the Deep Carbon Cycle:

1. Carbon Subduction:
   Carbon from the surface is drawn into the Earth’s interior through subduction zones, where tectonic plates meet. One plate slides beneath another, carrying carbon-rich materials such as carbonates and organic matter deep into the mantle. These materials are stored in the mantle for millions of years before being released through volcanic eruptions.

2. Volcanic Outgassing:
   Volcanoes play a crucial role in the deep carbon cycle by acting as release valves for carbon stored deep within the Earth. When tectonic plates move and magma rises, carbon dioxide (CO2) trapped in the mantle is released into the atmosphere through volcanic eruptions. This release of CO2 is a natural mechanism that regulates atmospheric carbon levels over time.

3. Plate Tectonics and Carbon Movement:
   The movement of tectonic plates is central to the deep carbon cycle. When plates collide and one is forced into the mantle, carbon is carried deep within the Earth. Over time, this carbon can remain stored for millions of years before it is released back into the atmosphere through volcanic activity. This process of subduction and volcanic eruption maintains a balance between the Earth’s interior and surface carbon.

Why Is the Deep Carbon Cycle Important?
The deep carbon cycle is critical for maintaining the Earth’s climate and supporting life. By controlling the flow of carbon between the Earth’s surface and interior, this cycle helps regulate global temperatures, prevent climate extremes, and ensure the stability of atmospheric CO2 levels. Without the deep carbon cycle, carbon could accumulate in the atmosphere or be trapped in the Earth’s crust, leading to drastic shifts in climate.

The Role of Volcanic Activity in Climate Regulation:
Volcanic eruptions are one of the primary ways that carbon is transferred from the Earth’s interior to the surface. However, volcanic activity does more than just release carbon dioxide; it can also influence short-term climate patterns. Large volcanic eruptions eject particles into the atmosphere, which reflect sunlight and can cause temporary cooling effects. This cooling influence, combined with the long-term release of CO2, helps maintain climate stability on a global scale.

How the Deep Carbon Cycle Affects Earth’s Climate:
While the deep carbon cycle operates on a geological timescale, its impact on Earth’s climate is significant. The amount of carbon dioxide in the atmosphere directly affects global temperatures, and the deep carbon cycle plays a key role in maintaining this balance. When volcanic activity releases CO2 into the atmosphere, it can trigger periods of warming. Conversely, when volcanic activity decreases, atmospheric CO2 levels fall, leading to cooling periods. This process helps to stabilize the Earth’s climate over millions of years.

Human Influence on the Deep Carbon Cycle:
While the deep carbon cycle operates naturally over millions of years, human activities are altering the carbon balance on a much shorter timescale. The burning of fossil fuels, deforestation, and industrial activities are releasing vast amounts of CO2 into the atmosphere at an unprecedented rate, disrupting the Earth’s natural carbon cycle. This increase in atmospheric carbon is accelerating climate change and shifting the balance of carbon on Earth. Understanding the deep carbon cycle is essential for developing strategies to mitigate these impacts and restore equilibrium.

How Scientists Study the Deep Carbon Cycle:
Studying the deep carbon cycle is a complex and ongoing process. Scientists use a variety of tools to investigate how carbon moves through the Earth’s interior, including seismic imaging, volcanic gas measurements, and laboratory simulations of high-pressure conditions. By examining volcanic rocks, mineral formations, and gas emissions, researchers can learn more about how carbon is stored, transported, and released within the Earth. This research helps scientists predict how the deep carbon cycle might evolve in the future and how it could impact global climate patterns.

Conclusion:
The deep carbon cycle is truly Earth’s hidden engine, working behind the scenes to regulate carbon storage, atmospheric CO2 levels, and climate stability. This natural process is essential for maintaining the conditions necessary for life on Earth. As human activities continue to disrupt the carbon balance, understanding the deep carbon cycle becomes more important than ever. By studying this hidden engine, we can gain a deeper understanding of our planet’s systems and better prepare for the challenges of climate change.

Twenty-eight DCO members came together from 29 April  –  4 May, 2018 at the Carnegie Institution for Science in Washington, DC to calculate a new estimate of global carbon dioxide (CO2) degassing from large volcanic emitters, small volcanic sources and diffuse degassing from volcanic regions. The synthesis of massive amounts of data was successfully tackled through a hands-on approach. Science talks were interspersed with breakout sessions, followed by more of the same.  “It was the most productive workshop I have ever attended,” said Terry Plank, DCO Executive Committee member and Reservoirs and Fluxes Science Community member (Columbia University, USA), “and should serve as a model for others to come.”

The DECADE synthesis workshop group attendees came prepared with a wealth of available volcanic emissions data they used to create a new global estimate.  Their work was exhaustive, with some of the highlights provided below.

The attendees evaluated emissions from subaerial volcanoes with active gas plumes to produce an updated and improved estimate of global SO2 flux. This quantity was then combined with their best present knowledge of C/S ratios in the plumes of those volcanoes to derive a corresponding emission of volcanogenic carbon.

They accounted for different types of emitters, including passively degassing volcanoes, explosive eruptions, and effusive eruptions and distinguished between arc and non-arc volcanic sources. They compiled data covering 11 years from 2005 to 2015, and used information from long-term monitoring from space (mostly OMI satellite) and ground (mostly NOVAC network), as well as short-term campaign data and reports from the literature. The group also identified the need for further comparisons between satellite- and ground-based flux observations and the lack of C/S data, in particular for large eruptions.

To improve estimates from small volcanic sources, they assembled a new compilation of worldwide data from more than 40 volcanoes that emit small CO2 plumes and carefully selected appropriate volcanoes to include in the extrapolation.  The group then individually reviewed more than 750 volcanoes from across the globe that could potentially host small plumes and categorized their emissions as ‘magmatic’, ‘hydrothermal’, or ‘none’.  Said Tobias Fischer (University of New Mexico, USA), one of the initial workshop organizers, “When complete, this analysis will be the most rigorous and transparent estimate of global CO2 emissions from small volcanic sources yet determined.”

Attendees also delivered the first estimate of global carbon dioxide (CO2) degassing from diffuse degassing sources of volcanoes based on the published data reported in MaGa, a recent catalogue of diffuse gas emissions around the world, while also addressing uncertainties of the data.  Other attendees analyzed subduction data that were providing insights into volatile cycling on both regional and global scales, while others considered what could be learned from the rock record.

Overall, the results from this workshop will provide new and more rigorously constrained global deep carbon emission estimates, new insights into the fate of subducted carbon and new methods for estimating volcanic CO2 fluxes through time using petrologic parameters. The workshop also highlighted the need for continued multi-disciplinary efforts in the area of volcanic and tectonic degassing to advance understanding of the transfer of volatiles between Earth’s reservoirs.

A joint study between Carnegie and the Woods Hole Oceanographic Institution has determined that the average temperature of Earth’s mantle beneath ocean basins was about 110 degrees Fahrenheit (60 Celsius) higher than previously thought, due to water present in deep minerals. The results are published in Science.

Earth’s mantle, the layer just beneath the crust, was the source of most of the magma that erupts at volcanoes. Minerals that make up the mantle contain small amounts of water, not as a liquid, but as individual molecules in the mineral’s atomic structure.  Mid-ocean ridges, volcanic undersea mountain ranges, are formed when these mantle minerals exceed their melting point, become partially molten, and produce magma that ascends to the surface. As the magmas cool, they form basalt, the most-common rock on Earth and the basis of oceanic crust. In these oceanic ridges, basalt can be three to four miles thick.

Studying these undersea ranges can teach scientists about what was happening in the mantle, and about the Earth’s subsurface geochemistry.

One longstanding question has been a measurement of what’s called the mantle’s potential temperature. Potential temperature was a quantification of the average temperature of a dynamic system if every part of it were theoretically brought to the same pressure. Determining the potential temperature of a mantle system allows scientists better to understand flow pathways and conductivity beneath the Earth’s crust. The potential temperature of an area of the mantle can be more closely estimated by knowing the melting point of the mantle rocks that eventually erupt as magma and then cool to form the oceanic crust.

In damp conditions, the melting point of peridotite, which melts to form the bulk of mid-ocean ridge basalts, was dramatically lower than in dry conditions, regardless of pressure. This means that the depth at which the mantle rocks start to melt and well up to the surface will be different if the peridotite contains water, and beneath the oceanic crust, the upper mantle was thought to contain small amounts of water—between 50 and 200 parts per million in the minerals of mantle rock.

So lead author Emily Sarafian of Woods Hole, Carnegie’s Erik Hauri, and their team set out to use lab experiments in order to determine the melting point of peridotite under mantle-like pressures in the presence of known amounts of water.

“Small amounts of water have a big effect on melting temperature, and this was the first time experiments have ever been conducted to determine precisely how the mantle’s melting temperature depends on such small amounts of water,” Hauri said.

They found that the potential temperature of the mantle beneath the oceanic crust was hotter than had previously been estimated.

“These results may change our understanding of the mantle’s viscosity and how it influences some tectonic plate movements,” Sarafian added.

The study’s other co-authors are Glenn Gaetani and Adam Sarafian, also of Woods Hole.

This research was funded by the National Science Foundation and the Woods Hole Oceanographic Institution’s Deep Ocean Exploration Institute.

The atmosphere that allows our planet to sustain life formed from gases emitted by volcanoes early in Earth’s history. These volatile elements are constantly recycled back into the deep Earth at subduction zones, where tectonic plates sink into the mantle. During this process the sinking plate was subjected to increasing heat and pressure, and releases volatiles. These volatiles, once added to the mantle, induce melting and fuel volcanic explosions, completing the cycle. While this depiction of the earth’s giant recycling factory was well established conceptually, they do not know how efficient it is. They can estimate how much goes in, but have little idea what proportion was released back to the atmosphere, and what proportion remains trapped at depth. This question was crucial if they want to understand how our atmosphere formed and our planet became able to sustain life. In the present-day context, characterizing how much gas comes out of the giant recycling factory was also key to understanding volcanic effects on climate, volcanic emissions being significant – but poorly constrained – parameters in current climate models..

Their team of early career volcanologists was conducting expeditions to the South American Andes. Their objective was to provide the first accurate and large-scale estimate of the flux of volatile species (H2O, H2, CO2, CO, SO2, H2S, HCl, HF, and more) emitted by volcanoes of the Nazca subduction zone. The journey was taking us across half a continent, from the giant volcanoes of Ecuador through the altiplanoes of Peru and to the Southern tip of Chile, traveling on some of the Earth’s highest roads, and climbing some of the Earth’s tallest volcanoes.

Even though carbon was one of the most abundant elements on Earth, it was actually very difficult to determine how much of it exists below the surface in Earth’s interior.

Research by Deep Carbon Observatory scientists Marion Le Voyer, Erik Hauri (Carnegie Institution for Science, USA), Katherine Kelley (University of Rhode Island, USA) and Elizabeth Cottrell (Smithsonian Institution, USA) has doubled the world’s known finds of mantle carbon. Their findings, based on analyses of crystals containing mantle magma samples, are published in Nature Communications.

Overall, there was a lot about carbon chemistry that takes place below Earth’s crust that scientists still don’t understand. In particular, the amount of carbon in the Earth’s mantle has been the subject of hot debate for decades. This topic was of interest because the amount of carbon present in the mantle underpins our planet’s geological processes, including triggering volcanic activity and sustaining the biosphere. It also affects our atmosphere when carbon dioxide gas was released by eruptions; volcanic eruptions played a large role in pre-historic climate variations.

But it’s difficult to measure the amount of carbon that exists below the Earth’s surface. Scientists can study the igneous rocks that formed when mantle melts, called magma, rose to the surface, erupted as lava, and hardened again to create a rock that was called basalt. However, the process of ascent and eruption releases almost all the magma’s carbon as carbon dioxide gas, which makes the erupted basaltic rocks poor indicators of the amount of carbon that was in the magmas from which they formed.

“This is how explosive eruptions happen,” Hauri explained. “The sudden catastrophic loss of gas that, before the eruption, was dissolved into the magma at high pressure, but during eruption has nowhere else to go, leaving no post-eruption trace in the hardened basalt of the amount carbon once present.”

But Le Voyer, Hauri, and their team analyzed some basalt samples from the equatorial mid-Atlantic ridge that contained previously unstudied tiny magmatic inclusions, small pockets of pure magma that were completely trapped inside solid crystals that protected them from degassing during magma ascent and eruption. Analysis showed that these inclusions had trapped their original carbon content before being erupted on the seafloor.

“This is only the second time that samples of magma containing their original carbon content have ever been found and analyzed, doubling our knowledge of the region’s carbon chemistry,” Hauri said.

The very first samples containing their original carbon were also revealed at Carnegie, by Hauri and Brown University professor Alberto Saal, in 2002. Those samples came from the Pacific seafloor. Comparison of the data for these two samples revealed that the mantle’s carbon content was much less uniform than scientists had previously predicted, varying by as much as two orders of magnitude in different parts of the mantle.

“Our discovery that mantle carbon has a more complex distribution than previously thought has many implications for how mantle processes may vary by location,” added Le Voyer, who conducted this research as a postdoc at Carnegie and was now at the University of Maryland.

When volcanoes erupt, they spew lava, ash, and gas into the atmosphere and over the surrounding landscape. The impacts of volcanic eruptions in populated areas are well documented, since scientists can monitor gas emissions and collect physical samples with relative ease. However, a significant fraction of Earth’s volcanoes are remote, making direct observation challenging.

Some researchers have therefore turned to space-based techniques, collecting data from satellites. In a new paper published in the journal Nature Communications, DCO collaborators Brendan McCormick Kilbride, Marie Edmonds (both at the University of Cambridge, UK), and Juliet Biggs (University of Bristol, UK), analyzed several sets of satellite data in order to reconcile, for the first time, geophysical and geochemical models of magma composition [1].

“We’ve known for some time that when many volcanoes erupt we see a change in elevation, like the volcano has deflated, and we can measure this change using satellite observations,” said Edmonds, co-Chair of DCO’s Reservoirs and Fluxes Community. “We also know that volcanic eruptions produce gas plumes rich in sulfur dioxide, which we can also measure from space. However, what’s been a bit of a mystery is how these two datasets fit together. We couldn’t spot a pattern.”

By measuring how much a volcano deforms throughout an eruption, scientists can make an estimate of the volume of material previously contained within the magma chamber. These measurements, however, were at odds with the mass of sulfur dioxide measured in the erupted gas plume.

“We were seeing way more sulfur dioxide than we would expect for the volume of materials expelled during an eruption,” said first author McCormick.

The team therefore began modeling what was going on beneath the surface. They found that if more gases like sulfur dioxide and carbon dioxide are present in magma, they change its physical properties. Magmas with high concentrations of these volatiles are not homogenous. Instead, the gases clump together, creating bubbles. These bubbly, spongy magmas are a lot more compressible than magmas without bubbles, partially explaining why many large eruptions rich in sulfur dioxide show only limited changes in ground deformation.

The authors also suggest that in eruptions with huge gas emissions, a fraction of pure gas could collect at the top of the magma chamber prior to eruption making the ratio of erupted gas to eruption volume even larger.

“What we’ve done here is build a model of volcanic eruptions that could explain several aspects of volatile rich magmas,” added McCormick. “We’ve shown that our model is consistent with several datasets. If we can confirm this relationship between sulfur dioxide output and eruption volume, we come closer to being able to use satellite data alone to investigate some of Earth’s most remote volcanoes.”

“These data also tell us a lot about the Earth system,” added Edmonds. “As we refine our model, and integrate data from DCO’s DECADE volcano monitoring stations, we’ll generate a much more accurate picture of deep volatile cycles, including the deep carbon cycle.”

Turrialba volcano had deposited ash on the capital city of Costa Rica and its 3 million inhabitants numerous times since 2014.

In a new article in the Journal of Geophysical Research and an online Earthchem database, a DCO-DECADE team led by Maarten de Moor (National University, Costa Rica) and Alessandro Aiuppa (Palermo University, Italy) tracked changes in gas composition and flux from 2014 to present [1,2]. The near-continuous and high-frequency gas monitoring time series (Multi-GAS and scanning DOAS stations) reveal a volcano in a state of extreme turmoil, posing an increasing threat to local lives and livelihoods.

During the monitoring time period the deployed instruments recorded large changes in gas composition and flux. Carbon dioxide to sulfur ratios show significant variations with notable peaks that occur weeks to days before eruptive episodes. The precursory spikes in carbon dioxide are the result of pulses of deep magma injected into the volcanic system. These rising magma bodies are directly responsible for the timing and magnitude of Turrialba’s eruptive periods. The hydrogen sulfide to sulfur dioxide ratio also displays remarkable changes over two orders of magnitude during the monitoring period, from constituting a major component of the bulk gas early in the time series to being undetectable by the Multi-GAS station. The disappearance of detectable H₂S in the gas emissions indicates the progressive boiling off of what must be an enormous hydrothermal system as magma intrusions invade the volcanic edifice, and a transition to purely magmatic gas compositions.

Perhaps most interesting for understanding the deep carbon cycle, the authors’ estimations of CO₂ flux from Turrialba suggest the most voluminous release of carbon dioxide did not occur at the same time as magma intrusion. Rather, they saw the release of huge amounts of CO₂ well after the first magma intrusion event, an observation also associated with high H₂S emissions. This suggests that a major proportion of CO₂ released over the three-year period was actually hydrothermal in origin, with deeply derived CO₂ stored in the hydrothermal system for an indeterminate amount of time and then released into the atmosphere during energetic explosions.

Decompression degassing modelling and analysis of the CO₂-SO₂-H₂S-H₂O system allowed the authors to estimate magma depth. The long time series of SO₂ emission rate allowed them to calculate the total volume of magma intruded since the beginning of Turrialba’s unrest. Importantly, the large variations in both gas composition and CO₂ flux highlight the need for continuous gas monitoring to define the carbon budget of convergent margins. These results once again show the potential power of high-frequency gas monitoring for forecasting eruptions.