A Sicilian volcano is blowing smoke rings in the sky. What are volcanic vortex rings?

But first, the setting — what and where is Mount Etna?

Mount Etna, sometimes referred to simply as Etna, is an active volcano on the east coast of Sicily, the largest island in the Mediterranean Sea, lying just off the toe of the Italian “boot”. Etna’s peak is the highest in Italy south of the Alps, and it is Europe’s largest and one of the most active volcanoes.

Etna’s summit has five craters, which are responsible for most of the volcano’s eruptions; there are also “flank” eruptions that occur out of 300-odd vents of varying sizes along the slopes of the mountain.

Etna is in almost constant activity, and has seen, since the year 1600, at least 60 flank eruptions and many more summit eruptions. In recent years, summit eruptions have occurred in 2006, 2007-08, on two occasions in 2012, in 2018, and 2021; flank eruptions have taken place in 2001, 2002-03, 2004-05, and 2008-09.

Etna has been a World Heritage Site since 2013, and according to UNESCO, the volcano’s eruptive history can be traced back 500,000 years. At least 2,700 years of this activity has been documented.

And what are volcanic vortex rings?

Vortex rings are generated when gas, predominantly water vapour, is released rapidly through a vent in the crater. The vent that has opened up in Etna’s crater is almost perfectly circular, so the rings that have been seen above the mountain since April 2 are also circular.

A scientific paper published on volcanic vortex rings in February 2023 noted that the phenomenon was first observed at Etna and Vesuvius in Italy in 1724, and has been documented in an engraved plate from 1755.

In more recent times, volcanic vortex rings have been observed at volcanoes such as Redoubt in Alaska, Tungurahua in Ecuador, Pacaya in Guatemala, Eyjafjallajökull and Hekla in Iceland, Stromboli in Italy, Aso and Sakurajima in Japan, Yasur in Vanuatu, Whakaari in New Zealand, and Momotombo in Nicaragua. (‘Dynamics of Volcanic Vortex Rings’: Scollo et al., Scientific Reports)

Simona Scollo, a volcanologist at the INGV Etna Observatory in Catania, Sicily and a co-author of the 2023 study, told The New York Times that volcanic smoke rings were produced in the same way as dolphins blow bubble rings. “They compress the water in their mouths, and using their tongue they push it out of their mouths and create such a pressure that it forms a ring,” Scollo told The NYT.

According to the report, the rings can remain in the air for up to 10 minutes, but tend to disintegrate quickly if conditions are windy and turbulent.

Is Etna well known for this phenomenon?

Yes. In July 2023, volcanologist Boris Behncke reported seeing “dozens of gas rings every day” above Etna. After this month’s phenomenon began, Behncke said on Facebook that “no volcano on Earth produces as many vapour rings as Etna”.

Since about one week, #Etna is releasing dozens of gas rings (also called “volcanic vortex rings”) every day. They come from a narrow vent in the SE part of the Bocca Nuova crater, one of the four active summit craters of the volcano, the same vent described in my previous post. pic.twitter.com/TJ2P3yEgVn

— Boris Behncke (@etnaboris) July 23, 2023

The rings, Behncke posted on X last year, “are produced by the explosion of gas bubbles within a narrow conduit, which shoots the gas at high speed toward the surface. Attrition along the conduit walls slows the movement of the gas jet, relative to the center of the conduit”.

Volcanic vortex rings are “not as rare as is often said”, and “Etna is a particularly prolific producer of such rings”, Behncke said in a linked post.

Gas rings are not as rare as is often said, and #Etna is a particularly prolific producer of such rings. In the year 2000 the same vent in the Bocca Nuova produced at least 5000 gas rings – and at the same time, more than 60 paroxysms occurred at the Southeast Crater … pic.twitter.com/QXnFX3NYtf

— Boris Behncke (@etnaboris) July 23, 2023

About the latest phenomenon, Behncke, who posted a video of Etna on Facebook, said: “…Now Etna is breaking all previous records. In the late afternoon of April 2, 2024, a small mouth opened on the northeastern edge of the Southeast Crater, producing gusts of incandescent gas. The next morning it was obvious that these blows were producing an impressive amount of steam rings, and the business has since been going on, having already issued hundreds if not thousands of these pretty rings.”

Does this mean Etna is about to erupt very soon?

“No, no, no,” Scollo told The NYT when asked if the activity meant Etna is going to erupt in a particularly spectacular way. In fact, the activity from the new vent was slowing down.

“It can stop because the properties of the conduit that allowed for the formation of these volcanic vortex rings can change, maybe with obstructions,” she told The NYT.