When volcanoes become metal

What would a volcano – and its lava flows – look like on a planetary body made mainly of metal? A pilot study from North Carolina State University provides insights into ferro-volcanism that could help scientists interpret landscape features in other worlds.

Volcanoes form when magma, which consists of the partially molten solids below the surface of a planet, erupts. On earth, the magma is mostly molten rock, which is largely composed of silica. But not every planetary body is made of rock – some can be mainly icy or even metallic.

“Cryovolcanism is volcanic activity in icy worlds, and we saw it happen on Saturn’s moon Enceladus,” said Arianna Soldati, assistant professor of marine, earth and atmospheric sciences at NC State and lead author of an article that works describe. “But ferro-volcanism, volcanic activity on metal worlds, has not yet been observed.”

Enter 16 Psyche, a 140-mile asteroid in the asteroid belt between Mars and Jupiter. According to infrared and radar observations, the surface is mainly iron and nickel. 16 Psyche is the subject of an upcoming NASA mission, and the asteroid inspired Soldati to reflect on what volcanic activity might look like in a metal world.

“When we look at images of worlds that are different from ours, we still use what is happening on Earth – like evidence of volcanic eruptions – to interpret it,” says Soldati. “However, we do not have a widespread metal volcanism on earth, so we have to imagine what those volcanic processes might look like in other worlds so that we can interpret images correctly.”

Soldiers define two possible types of ferro-volcanism: Type 1, or pure ferro-volcanism, which occurs on all-metal bodies; and type 2, false ferro-volcanism, which occurs on hybrid rocky metal bodies.

In a pilot study, Soldiers and colleagues from the Syracuse Lava project manufactured type 2 ferro-volcanism, in which metal separates from rock as the magma forms.

“The furnace of the Lava project was set up to melt rock, so we worked on the metals (especially iron) that occur naturally in it,” says Soldati. “If your rock melts under the extreme conditions of the furnace, some of the iron will separate and sink down because it is heavier. By emptying the furnace completely, we could see how that metal magma behaves compared to the rock one. “

The metal lava flows traveled ten times faster and spread thinner than the rock, breaking into a multitude of braided channels. The metal also moves largely below the rock flow and comes from the leading edge of the rocky lava.

The smooth, thin, braided, widely distributed layer of metal lava would, according to Soldati, leave a very different impression on the planet’s surface than the often thick, coarse, rocky flow.

“Even though it’s a pilot project, we can still say a few things,” Soldati said. “If there were volcanoes on the 16 psyche – or on another metal body – they would certainly not look like the steep mountain Fuji, an iconic terrestrial volcano. Instead, they would probably have soft slopes and wide cones. It is how an iron volcano would be built – thin flows that extend over longer distances. ‘

The work appears in Nature communication.