Adding crushed volcanic rocks to the soil on farms can help sequester CO2

Farmers might possess a secret weapon in the fight against climate change. A recent study reveals that by simply incorporating crushed volcanic rocks into their fields, they could play a pivotal role in helping the planet achieve the carbon removal target set by the Intergovernmental Panel on Climate Change (IPCC).

According to the study published in the AGU’s journal Earth’s Future, the regions showing the most promise for this innovative climate strategy are the warm, wet tropics.

Termed “enhanced rock weathering,” this approach leverages the natural weathering process, which inherently captures carbon dioxide in carbonate minerals. The underlying concept is straightforward.

Accelerate weathering in a manner that simultaneously aids humans simply by adding volcanic rocks to agricultural fields. If adopted alongside emissions reductions, this technique could act as a brake on the rapid acceleration of global warming.

S. Hun Baek is a Yale University climate scientist and the study’s lead. He remarked, “Enhanced rock weathering poses fewer risks compared to other climate interventions.”

He further highlighted its additional perks, stating, “It also provides some key benefits, like rejuvenating depleted soils and countering ocean acidification, that may make it more socially desirable.”

Studying enhanced rock weathering

The focus of this study was the utilization of crushed basalt, a rapidly weathering rock originating from cooled lava. By evaluating the efficiency of various regions in decomposing these rocks, the researchers aimed to pinpoint the best areas for its application.

Geochemist Noah Planavsky, a co-author of the study from Yale University, emphasized the significance of this discovery, stating, “There’s tremendous potential here.” He elaborated on the need to dive deeper into the basics, while also exploring market and financial angles.

In contrast to an earlier study that set its sights on estimating carbon drawdown by 2050, this study ventured beyond national boundaries and peered further into the future.

Researchers employed a novel biogeochemical model to gauge the impact of applying crushed basalt on global farmlands. This model simulated the process of enhanced rock weathering across 1,000 agricultural sites worldwide, spanning from 2006 to 2080.

Volcanic rocks and global farmland

Astonishingly, the findings revealed that in just 75 years, these sites could reduce atmospheric carbon dioxide by 64 gigatons. If we expand this approach to all farmlands globally, we could lock away a staggering 217 gigatons of carbon.

“To put it in perspective,” Baek notes, “The latest IPCC report indicated a need to sequester between 100 to 1,000 gigatons of carbon by 2100, on top of substantial emissions reductions. Our estimates, when applied globally, roughly align with the lower end of this bracket, boosting our hopes of meeting these climate targets.”

Best results from tropical weather

The study also found that due to the speedier weathering process in hot and moist conditions, tropical regions would see faster results compared to areas closer to the poles. For those contemplating carbon sequestration investments, tropical fields would be an efficient choice.

Additionally, the research presented a silver lining. Enhanced rock weathering might prove more effective under warmer conditions. Contrarily, several other carbon reduction methods lose their efficacy as temperatures continue to soar.

Baek emphasized this resilience against climate change, stating that it remains “relatively insensitive to climate change and works about the same under moderate and severe global warming scenarios.”

Interestingly, many farmers already enrich their fields with limestone. Transitioning to a different rock type might be a seamless shift, paving the way for enhanced rock weathering to be implemented extensively, opined Planavsky.

With several farms globally having experimented with this method on a small scale, the next logical step, according to Planavsky, is to focus on “realistic implementation.”

More about volcanic rocks

Volcanic rocks are igneous rocks that form when magma from a volcano cools and solidifies, either within the Earth (intrusive) or on the surface (extrusive). Here’s a comprehensive overview of volcanic (or extrusive) rocks:

Formation

Volcanic rocks primarily form from the cooling and solidification of molten lava ejected from volcanoes. The rate at which this lava cools can influence the texture and mineral content of the rock.

Texture

Aphanitic rocks have fine-grained textures, often due to rapid cooling at or near the Earth’s surface. Individual minerals can be hard to distinguish with the naked eye.

Porphyritic rocks have a mixed texture. A finer-grained matrix (groundmass) holds large crystals (phenocrysts). This indicates a two-stage cooling process.

Vesicular are rocks with many cavities, or vesicles, created by gas bubbles in the molten lava. Pumice is a classic example.

Types of volcanic rocks

Basalt rocks are dark-colored and fine-grained. Basalt is the Earth’s most abundant volcanic rock. It’s often found in oceanic crust and volcanic islands. Andesite rocks are intermediate in composition between basalt and rhyolite. Volcanic arcs above subduction zones typically contain andesite.

Rhyolite rocks display a light color and often possess a very fine-grained or glassy texture. Rhyolite is rich in silica. Pumice is a type of rhyolite. This rock is so vesicular and light that it can float on water. Scoria rocks are dark and vesicular. They are more dense than pumice but less dense than basalt. Researchers often find scoria rocks in basaltic and andesitic terrains.

Obsidian rocks are a naturally occurring volcanic glass formed by rapid cooling of silica-rich lava. They are often black, but can also be red or green. Tuff rocks are formed from volcanic ash. They can be welded (if hot when deposited) or non-welded.

Mineral composition

The mineral content of volcanic rocks can vary, but they often contain minerals like plagioclase, pyroxene, olivine, and amphibole.

Plate tectonics

The type and location of volcanic rocks can tell geologists about tectonic settings. For instance, mid-ocean ridges and oceanic islands (like Hawaii) commonly have basalt. This indicates mantle-derived magmas. In contrast, andesite or rhyolite might form at continental margins above subduction zones.

Importance in soil formation

Over time, volcanic rocks weather and break down to produce rich, fertile soils. Regions with a history of volcanic activity, like parts of Italy, are renowned for their fertile lands, which are conducive to agriculture.

Cultural and practical uses

Various cultures have used obsidian to produce sharp-edged tools and weapons. Manufacturers use pumice as an abrasive, in lightweight construction materials, and to stone-wash jeans. People use basalt in construction, and it is also the primary material for manufacturing oceanic crust and conducting seafloor spreading studies.

Ecological importance

Volcanic rocks, especially in freshly erupted terrains, provide a unique ecological niche. Certain organisms, particularly lichens and some hardy plants, colonize these areas, kickstarting the process of ecological succession.

Health impacts

Inhaling fine volcanic ash (which can be a component of tuff) can be harmful to health, particularly for people with respiratory conditions.

Climate impacts

The eruption process can release vast amounts of gases like sulfur dioxide, which can influence global climates. For instance, large volcanic eruptions can lead to global cooling due to the injection of sulfate aerosols into the stratosphere, which reflect sunlight.

In a nutshell, volcanic rocks not only provide insights into the Earth’s internal processes and tectonic settings but also have ecological, economic, and climatic significance.

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