Etna Vortex Rings

One of the planet’s most famous and active volcanos sits on the island of Sicily, where the African and Eurasian Plates converge. Mt. Etna currently rises 11,014 feet (3,357 meters) above the Ionian Sea. It gains this altitude in under 12 miles from the water! The word “currently” must reside in the previous sentence thanks to Etna’s rambunctious nature. The volcano is so active that it gained 100 feet in height in six months during 2021!

One of the so-called Decade Volcanoes, Etna poses a massive risk to a large population. More than a million people live within dangerous proximity to potential lava flows, ash flows, and lahars. This mountain has posed an existential threat to humanity for as long as we have inhabited the Mediterranean.

Mt. Etna, with the city of Catania in the foreground - photo by BenAveling

Etna is a wonderful example of the type of duality we have encountered often during our exploration of the world, simultaneously beauty and menace. Though her exultations wreak destruction, they can also light the human imagination.

Recently, Etna replicated one of its greatest magic tricks: it blew smoke rings.

Etna smoke ring in 2023 - photo by Jpakkala
Smoke ring above Mount Etna in 2023 - photo by PSomol
The phenomenon in 2012 - photo by Angelosalemi

This incredible phenomenon resembles the cartoons and films that featured smokers creating pristine rings with their exhalations:

Technically, these emanations from Etna are not composed of smoke but steam and volcanic gas. They are an example of what scientists term vortex rings. A vortex is a region in a fluid that revolves around an axis line. Mathematicians call them toroidal vortices since the structures are torus-shaped (think the shape of a donut, though tori can take other forms). In vortex rings, the fluid spins around an axis to form a closed loop.

The rings often move perpendicular to the plane of the ring, which produces the nice upward motion we see over Etna. The rotational flow of the vortex reduces friction between the core and the surrounding fluid – in this case, the air – which allows the form to move large distances without dispersing or losing kinetic energy.

A ring torus - graphic by Watchduck
Flow around an idealized vortex ring - graphic by Lucas Vieira

The phenomenon is relatively common among fluids. However, we rarely see them because they usually do not contain suspended particles. Etna seems to be a master at belching toroidal vortices, but it is not the only volcano with the ability. Stromboli, a volcano north of Sicily, has produced the clouds, in addition to other volcanoes in Iceland, Alaska, Japan, New Zealand, Indonesia, Ecuador, Guatemala, and Nicaragua.

The volcanic vortex ring is rather striking, but it is not the only flavor nature has in its cookbook.

Mushroom clouds, formed by atomic or volcanic blasts, feature dual toroidal fireballs, producing perhaps the largest vortex rings. Meteorological microbursts – also known as downbursts – can make visible vortex rings. Some powerful artillery weapons can create them. Underwater, divers, dolphins, and whales sometimes beget bubble rings, the vortex rings in which air occupies the core while surrounded by water.

The toroidal guts of a mushroom cloud - graphic by Fastfission
A vortex ring from a weapon - photo by Spc. William Hatton
A scuba diver blows a bubble ring - photo by Jon Rasmussen
Beluga whales blowing bubble rings - photo by Pagemoral

Gandalf’s exploits with smoke are, as the kids say, cold, but purportedly fire eaters can also conjure vortex rings. I could not track down any footage worthy of sharing, but perhaps that will simply allow this fire vortex cannon to shine:

Even the human heart gets in on the vortical action. As blood enters the left ventricle, it forms a vortex ring!

Vortex rings in the human heart - Gharib, Rambod, et al.

While Etna could potentially bring catastrophe to the lives of many, the vortex rings it emits are undoubtedly enthralling. When the sunlight catches them correctly, you’d be forgiven for mistaking them for cherubic halos.

The natural world forges some wonderful chains for those enthralled with it. Etna spewing gorgeous rings leads us to Bilbo Baggins, mushroom clouds, dolphins blowing bubbles, and fire cannons. It even leads to a mesmerizing video of colliding rings that craft miniature vortices. This universe is truly a marvel!

Further Reading and Exploration

Mount Etna Puffs ‘Smoke Rings’ Into the Sky – Smithsonian Magazine

Rotational Flows: Circulation and Turbulence – UC Davis

The Physics of Vortex Cannons – Medium

Vortexes and Mushroom Clouds – The Physics Behind Life

Optimal vortex formation as an index of cardiac health – Proceedings of the National Academy of Sciences

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