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Screenshots below are from Bloomberg News' April 10, 2024 Italy's Mt. Etna Puffs Out Smoke Rings (also available at AP News' April 7, 2024: Mount Etna blows spectacular smoke rings into the sky). Some of the rings continue quite a long time and evolve into beautiful thin rings floating high into the sky.

Question: I'm curious, what morphological formations inside Etna allow it to produce such nicely formed smoke rings, and how common this phenomena is in volcanoes (has this been documents for Etna or other volcanoes before)?

Mt. Etna smoke rings 2024-04-05

Mt. Etna smoke rings 2024-04-05

Mt. Etna smoke rings 2024-04-05

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Is it new?

No! It's been witnessed for at least a few centuries (probably more, but we don't have records). According to Fuentes (2014):

Ignazio Sorrentino, secular priest of Torre del Greco and a keen student of Vesuvius, was the first to mention the occurrence of rings of volcanic ash in his book Istoria del Monte Vesuvio. He relates his first observation, made on 11 September 1724

Which also partly answers the "other volcanoes" part (see below for more). Like Etna, mount Vesuvius is known for its volcanic vortex rings (VVRs, the "official" name of smoke rings). Another early account was made by naturalist Della Torre (1755) in Storia e fenomeni del Vesuvio, which contains this engraved plate by Giuseppe Aloja:

Engraved plate showing smoke rings at mount Vesuvius

An English translation of Della Torre's observations is given in Fuentes (2014).

Has this been documented for Etna before?

Yes. I don't think there is enough data to compute a frequency, but here are a few more occurrences. Still according to Fuentes (2014), smoke rings were observed at mount Etna in 1763, 1819 and 1842. Perret (1912) reported such rings during an eruption in 1910. According to volcanologist Boris Behncke, an Etna expert, the volcano did no less than 5,000 VVRs in 2000! A friend of mine sent me nice VVR photos he took on Etna in 2023. So it's relatively common. I'm not sure why there's been such a crazy media rush on this story lately...

Has this been documented for other volcanoes before?

Yes! We already mentioned Vesuvius and Etna, but there are more. In a recent article about the phenomenon (Pulvirenti et al., 2023), Table 1 is a "list of volcanoes that have produced vortex rings". The list contains: Aso, Eyjafjallajökull, Hekla, Momotombo, Pacaya, Redoubt, Sakurajima, Stromboli, Tungurahua, Yasur, Whakaari. A number relatively low compared to the hundreds of active volcanoes listed by the Global Volcanism Program.

What morphological formations inside Etna allow it to produce such nicely formed smoke rings?

As for the formation of VVRs, it's been studied for a while, and reproduced by both analog experiments and numerical simulations. Fuentes traces this study back to a 1858 paper by Helmholtz! According to the latest research, Pulvirenti et al. (2023), VVRs are generated when gases are expelled from a circular vent due to the application of an impulsive overpressure, attributed to a gas slug explosion under a solidified magma plug, which is summarized by this cartoon:

Scheme showing the steps leading to the formation of Volcano Vortex Rings

Scheme showing the steps leading to the formation of Volcano Vortex Rings, CC BY Pulvirenti et al. (2023)

Mount Etna has a perfect vent for this: its Bocca Nuova ("New Mouth") is circular, is clogged by a solid magma plug, and has gas flowing between this plug and the conduit walls, as showed on this diagram (which was meant to show that gas is also flowing through "pit craters", but nicely illustrate the overall shape of the vent):

enter image description here Simplified scheme of Bocca Nuova's feeding system in July 2023, CC BY-ND Marco Neri/INGV.

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    $\begingroup$ This is really beautiful, thank you! $\endgroup$
    – uhoh
    Commented Apr 15 at 21:38
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    $\begingroup$ You're welcome! I've never witnessed them myself (yet) but VVRs have been a fascinating topic to me for a while! (like all things volcanics...) $\endgroup$ Commented Apr 16 at 19:17

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