What defines a volcano?
Many are fueled by the embers leftover from the dawn of the solar system, or by heat emitted from radioactive decay. Some are powered by tides created by monstrous gravitational forces. Each one has a unique personality and distinctive architecture. They are all built differently, come in all shapes and sizes, and appear on all sorts of planets and moons. No two volcanoes are alike.
Ultimately, their definition comes down to what every single volcano does: at some point, pressurized molten matter erupts out of a chasm, spilling onto the surface of the world or simply shooting off into space. Those eruptions often involve liquid rock. In some places, including the dwarf planet Ceres, Saturn’s moon Enceladus, Neptune’s Triton, and Pluto, you get cryovolcanism, where slushy ices take on the role of classic lava.
But what about liquid metal? Scientists suspect that being a fairly common component of the cosmos, molten iron must be erupting from volcanoes somewhere out there. But to date, ferrovolcanism, as it’s technically known, has yet to be spotted. Fortunately, volcanologists are an impatient bunch. A few of them got bored of waiting and decided to make their own heavy metal lava flows simply to see what they looked like.
To their delight, they look extremely weird.
Typical lava flows are, for the most part, easy to outwalk. But these ferrous flows move like they are desperate to evade capture. They meander about in a speedy, menacing manner. On one of the videos showcasing these iron lava flows, you can hear the crowd standing around it and gasping, whooping, and laughing. The sheer strangeness of the spectacle caused one of them to say “no, that’s not okay.”
“It definitely has that wow factor,” says Brandon Johnson, a planetary scientist at Purdue University who wasn’t involved with the work. Johnson explains that he showed a video of one of the iron lava flows to his five-year-old son who enthusiastically agreed that it was exceedingly cool.
Editor note: Supercluster agrees.
But there is more to these experiments than visceral volcanological thrills. Until a robot or astronaut gets to investigate a suspicious site up close, planetary scientists rely on telescopes and spacecraft spying space volcanoes from afar. Plenty of far-flung geologic formations look puzzling at first, so scientists have to rely on what they already know as they attempt to identify them.
“We use what we find on Earth to interpret what we see on other planets,” says Arianna Soldati, a volcanologist at North Carolina State University and the study’s lead author. Now that we know what ferrovolcanic flows actually look like, we can try to find them off-world.
The research was conducted at Syracuse University’s Lava Project. A collaboration between sculptor Bob Wysocki and geologist Jeff Karson who are known as the folks that grilled some steak over lava. They make that lava themselves: they put volcanic rock in a crucible, cook it at 3,000 degrees Fahrenheit within a great big furnace, then pour it out and see what transpires. It not only looks badass, but it’s also a fantastic way to study the behavior of lava flows and to see what happens when they meet things like ice or water.
As one of the many volcanologists enamored by the Lava Project’s experiments, Soldati found herself gazing at a hypnotic flow one day when she noticed something curious. Melting rock takes a lot of energy, so once it’s molten you want to keep it molten. That means the furnace is often ablaze for an entire week, during which time all the lava within is unleashed through multiple pours. And during the final pour, and the final pour alone, a bizarrely thin and quick flow scoots forth.
Naturally, Soldati wanted to know what the heck was happening — and it turns out that there is some freaky chemistry going on.
That hefty lava-containing crucible is made of silicon carbide, and when it’s flambéed the carbon in it escapes. That means that it has a limited shelf life. “The crucible lasts for a few cycles of experiments, but at some point, it becomes thin and it just cracks,” says Soldati.
The escaping carbon deoxygenates its surroundings, both by reacting with oxygen to make carbon monoxide and by physically pushing oxygen out of the furnace. The naturally occurring iron in the volcanic rock likes being bound to oxygen, which allows it to stay in the molten soup as part of the lava. But if you remove enough oxygen, the iron turns into its pure metallic form. It’s really dense, so it sinks to the bottom of the crucible, ensuring it is always the last thing to be poured out of the crucible.
“And that’s when I made the connection,” says Soldati: the Lava Project had been making ferrovolcanic flows by accident all this time. Until now, no one had paid them much attention, but she reasoned that these lava latecomers could be used to investigate how iron flows behave. Her team got to work and documented them, reporting their findings in the journal Nature Communications in March.
As a final pour is made, the usual last gasp of molten rock spills onto the ground, moving just under a tenth of a mile per hour. At the very last moment, and accompanied by a dramatic flourish of sparks, molten metal tips over the spout.
A small volume of liquid iron snakes across the top of the molten rock as narrow rivers flowing ten times faster than that underlying lava. Despite initially being a whopping 2,200 degrees Fahrenheit, these rivers rapidly cool and solidify before the snail-like shimmying of the ropey lava below snaps them into pieces. Most of the liquid iron, though, sinks into the lava. It bunches up toward the front of the lava flow before exploding out of it as braided, winding streams — silvery strokes of an altogether alien calligrapher.
“You see metal moving out, and it’s moving really fast and you’re not expecting it. It’s exciting!” says Soldati. “I kind of jumped back. My thought process was: if this stuff gets on my toes, this is bad.”
On the back of this work, Soldati and her colleagues have sketched out two broad categories of ferrovolcanism. The first is the ‘pure’ type: like the experiments’ braided streams that flow independently in front of the normal lava flows, these are the sort that erupt on entirely metallic worlds.
Such a process is thought to have transpired on Psyche, a 155-mile wide metal sphere in the asteroid belt. This object was once an embryonic planet, but a series of violent collisions stripped away the silicate shell, leaving the iron-nickel core behind. As that core cooled, scientists suspect that molten iron erupted out of cracks on the surface.
NASA is launching a spacecraft to Psyche next year to study this exposed planetary core. It probably won’t have active ferrovolcanism anymore, and the surface has been so smashed up over the eons that evidence of ancient iron lava flows is likely to have been erased. I’d be quite floored it if turns out we see these ferrovolcanic flows,” says Johnson, who has mathematically modelled the phenomenon. “But stranger things have happened.”
A better bet may be found closer to home. Rocky worlds are often built on a foundation of basaltic volcanism, a type of fiery landscaping that features iron. If starved of oxygen, that iron may sink away from the buoyant molten rock, waiting until a tectonic squash squeezes it out as an eruption. This, the second type of feerrovocanism, is known as ‘spurious’ ferrovolcanism, something represented in the experiments by those iron rivers that move about within the normal lava flow.
Mars has a lot of iron in its volcanic rocks, so, Soldati speculates, perhaps the red planet is a good place to search for evidence of ancient iron eruptions. We may even have seen metal volcanism on Earth: odd frozen bands of magnetite — an iron ore — in El Laco, Chile, have been suggested as being possible ferrovolcanic flows.
One day, somewhere out there, a definitive iron lava flow will be found. Until then, these experiments will continue, helping scientists understand how the solar system’s more exotic volcanoes make the canvases of their worlds. Mathematical models have clear scientific merits, but as this sort of practical work demonstrates, sometimes you have to shrink the universe down to size to get a better grasp of reality.
“It’s one thing to calculate it and think about it,” says Johnson. “It’s another thing to see it happen.”