Explosive volcanic eruptions can remove carbon from the atmosphere

Pierre Delmelle (ELI), Sébastien Biass (University of Geneva), Mathilde Paque (ELI), and Benjamin Lobet (ELI) have just published an article entitled "Explosive volcanic eruptions can act as carbon sinks" in the prestigious journal Nature Communications.

Active volcanoes are generally perceived as sources of CO₂, but they can also trap it! This is the finding of a study by Pierre Delmelle and his team. The scientists have shown that these eruptions can be ‘carbon negative’, storing up to 15 times more carbon than they release.

Active volcanoes are typically viewed as sources of CO₂, releasing the greenhouse gas during eruptions. However, a new study published in the journal Nature Communications by researchers from the Earth and Life Institute and the Department of Earth Sciences (University of Geneva, Switzerland) reveals a lesser-known effect of volcanic activity: explosive volcanic eruptions can actually help remove carbon from the atmosphere. 

When volcanoes erupt explosively, they deposit thick layers of ash, known as tephra. These tephra deposits typically serve as a substrate for the formation of volcanic soils, which have a remarkable capacity to accumulate and retain organic carbon. This carbon originates from plants that capture atmospheric CO₂ through photosynthesis. When plants die, a fraction of their carbon is stored in the soil as organic matter.

Measurements showed more carbon buried in the soil than released in the atmosphere

The research team, led by Prof. Pierre Delmelle, hypothesized that explosive eruptions not only create new carbon-rich volcanic soils but also bury existing ones, effectively locking away atmospheric carbon for millennia.

To test this idea, the team conducted fieldwork in the Ecuadorian Andes, where a region was blanketed ~2,270 years ago by tephra from a major explosive eruption. Their measurements showed that this eruption buried and preserved more carbon in the soil than it released into the atmosphere.

In Ecuador, a third of the country’s total soil carbon stock buried by explosive eruptions in the past 12.000 years

Building on these findings, the researchers developed a modelling framework to estimate how much organic carbon is buried in soils repeatedly affected by explosive eruptions over time. 

In Ecuador, even the most conservative estimates suggest that this process has sequestered enough organic carbon over the Holocene (the past ~12,000 years) to account for up to one-third of the country’s total soil carbon stock.

Remarkably, Pierre Delmelle and colleagues found that the amount of carbon stored in volcanic soils repeatedly affected by tephra exceeds the cumulative carbon emissions from the eruptions responsible for their burial by a factor of 3 to 15, effectively making these explosive events carbon-negative.

“We have long known that volcanoes outgas the Earth, but now we also need to consider how they may remove carbon from the atmosphere by trapping it in soils”, said Prof. Delmelle.

This research highlights the unexpected role that explosive volcanoes can play in the Earth’s carbon balance, not just as sources of CO₂, but as agents of long-term carbon storage.
 

This article was originally written by Pierre Delmelle. The AREC team of UCLouvain has also written an article in French. It is available to be read here.

You can read the press release here (french). It gave way to several press articles, notably in Le Soir and on the RTBF website.

Abstract

Volcanic soils, covering only ~1% of the Earth’s land, store over 5% of the global soil organic C stock. The frequent burial of these soils by tephra fallout from explosive volcanic eruptions is a critical but poorly quantified C storage process in soils from volcanically active regions. Using field measurements, we demonstrate that single eruptions can bury substantial amounts of stable organic carbon in soils. We develop a modelling framework and estimate that, in Ecuador alone, at least 1.1 Pg C has been stored in volcanic soils repeatedly affected by tephra deposition during the Holocene. This stock of tephra-buried soil organic carbon exceeds the cumulative CO₂ emissions from the source eruptions. Here, we show that explosive volcanism, through the repeated burial of organic C in volcanic soils, acts as a significant regional C sink over time, ultimately averaging to net C-negative events.

Reference

Delmelle, P., Biass, S., Paque, M. et al. Explosive volcanic eruptions can act as carbon sinks. Nat Commun 16, 4306 (2025). https://doi.org/10.1038/s41467-025-59692-4

The article is available in open access on the Nature Communications website.