Volcanic mountains

How volcanic eruptions help feed the world

Solange Duhamel turned her back to the wind as it almost sideways lashed the Icelandic rocky landscape last April. She shielded her face from the hailstones, waiting for the storm to end. Yet Duhamel couldn’t help but gaze in wonder at the scene unfolding in front of her.

A stream of glowing lava poured out of the mouth of the nearby Fagradalsfjall volcano, which had been erupting for weeks, almost filling the valley where Duhamel stood with jet black rock. When the hail collided with the still sizzling surface of the lava field, it instantly vaporized, rising in swirls of fog.

The misty cloak that covered the landscape only enhanced the otherworldly impression of the process that Duhamel, an environmental microbiologist and biogeochemist at the University of Arizona, came to study: The Birth of a New Earth. Many people see volcanic eruptions only as forces of death and destruction, and their capricious explosions can certainly wreak havoc. But eruptions also create a blank canvas that gives way to a rainbow of life.

Volcanoes have produced more than 80 percent rock on the surface of the Earth today, both above and below water, digging craters and building mountains, islands and plateaus. Eruptions extract nutrients from the bowels of our planet, spreading them through rock and ash which eventually breaks down, once on earth, into fertile soils. The steps to release these nutrients come from the combined efforts of wind, water, and microbes. Together, they transform the shades of gray of the volcanic landscape into rusty red and mustard yellow soils that soon explode with lush green vegetation.

A more subtle rainbow comes to life under certain volcanic surfaces. There, the underground cavities offer niches where germs can thrive, possibly partially fueled by nutrients and organic matter seeping in from above. Some of the colonies are visible to the naked eye, but ultraviolet light shines on the underground walls and a microbial galaxy erupts. “You can see small individual colonies and the films appear in glorious colors,” says Jen Void, astrobiologist at NASA’s Ames Research Center.

The violent awakening of the Fagradalsfjall volcano on March 19 gave Duhamel a golden opportunity to study one of the first stages in the transformation of lava: the microbial colonization of the cooled surface.

Cooled lava rock is initially sterile because it emerges from the earth at temperatures hotter than 2,000 degrees Fahrenheit, far too hot for life to survive. By collecting weekly surface samples, Duhamel and his colleagues hope to pinpoint what appears there and when. “It’s pretty rare to be able to study a volcanic eruption from the start,” she says.

Even when cooled, the cool expanses of lava rocks are not very welcoming to life. Volcanic ash and rocks are rich magnesium, iron, calcium, potassium and more, but these nutrients are not easily usable. Many ingredients essential for life, such as nitrogen, are also scarce, so pioneer microbes have to be resourceful. Some of the first drivers can be microbes that consume nitrogen from the air, converting this gas into forms that are easier to use for other organisms and setting the stage for later arrivals. “You can see it as a collaboration of life,” says Duhamel.

During this time, the rock and ash slowly begin to decompose, made visible by the chemical changes in the metals trapped inside. Particularly important is iron, which deteriorates into iron oxides, one of which is commonly referred to as rust. Wind and water partly cause the physical and chemical changes. But some microbes can also transform the metals in the rock. “Microbes, in many ways, are the painters here,” says the Boston University professor. Jeffrey Marlow, who is collaborating with Duhamel to study the microbial transformation of volcanic minerals.

The key to this colorful transformation is the rapid decomposition of volcanic glass, which forms when lava cools rapidly and forms both ash and parts of rock. Yet the rate at which volcanic soils form and the hue they take on also depend on temperature, water content, vegetation, etc. Red soils, for example, are often found where the land is dry and sparsely vegetated and the rocks are full of iron. In cool, humid environments with abundant plants, excess organic matter turns the soil yellow or brown.

Weathering gives way to waves of greater life forms. Lichens are usually the first to arrive in the form of mottled leaves and ruffles of dusty greens, vibrant oranges, mustard yellows. These organisms are actually a partnership between fungi and algae, which allows them to survive in harsh environments where plants often fail. Their tiny root-like structures generate acid which help break rock, preparing him for greater forms of life. Which starts out as small islands and patches that expand as they become more and more lush. “You will end up with a mosaic of different stages of succession”, explains Catalina González Arango, paleoecologist at the University of the Andes in Colombia.

Volcanic eruptions make a canvas not only for surface life but also for basement life. Basalt lava is poor in silica, which makes it flowable, as seen in Fagradalsfjall or Hawaii’s Kilauea. As molten rock flows like a river, the upper layers can cool down to form thick crusts that isolate the stream below. But if the flow is diverted or the rash ends, it leaves behind what is called a lava tube.

At first, the caves may seem like empty black envelopes, but close inspection reveals many subtle hues of microbes. In some tubes, colonies of Actinobacteria spread in thin golden biofilms that repel water, Blank says. Other microbes seem to grow with tiny white branches of “cave coral” or tawny polyps. Brilliant ultraviolet light reveals even more hidden diversity that shines in neon blues, oranges and greens.

The many colors of volcanoes, both above and below ground, reflect the collaboration of geology and life that has shaped our planet as we know it today. This interaction will likely continue for a long time into the future. It can also give clues to what lies beyond our home world, aiding scientists in their search for alien life. Maybe those scenes that seem so from another world could, in fact, be found on other worlds.

Maya wei haas is a science writer at National Geographic.

This story appears in the December 2021 issue of National geography magazine.