Friday, 31 March, 2000, 12:13 GMT 13:13 UK
Etna hoops it up
By BBC News Online science editor Dr David Whitehouse
Volcanologists have witnessed dramatic rings of steam and gas being blown out of volcanic vents on the side of mighty Mount Etna in Sicily.
Etna is the tallest and most active volcano in Europe, situated where the European and African geological plates are colliding.
Dr Jug Alean and Dr Marco Fulle have been investigating Etna's growing level of activity and in February they saw the ejection of several spectacular hoops from the Bocca Nuova region of the mountain.
"This wonderful specimen gently drifted overhead and past the Sun which was tinted orange by aerosols in the smoke," Dr Alean told BBC News Online.
It is difficult to gauge the size of what the scientists are calling "steam rings". They drift across the blue sky with no points of reference. However, the volcanologists estimate the hoops to be about 200m across and up to 1000m above the ground.
Stable shape
Smoke rings have been seen at volcanoes before but never in such detail. This time, there was hardly any ash on Etna and the gas billowing from vents had a high steam content. It is for this reason that Drs Alean and Fulle are using the term "steam rings".
Looking like the hoops produced by smokers, the hoops can hang in the air for many minutes. Etna's rings have been seen to last as long as 10 minutes.
How they are formed is a mystery that these pictures may help solve.
Dr Jurg Alean speculates: "They could be formed by rapid gas pulses emitted by narrow vents into the atmosphere. The physics seems somewhat complicated and I am trying to establish if there are sound scientific theories about them."
Drs Alean and Fulle keep a close eye on Etna, running a private seismic monitoring station as well as maintaining a photographic record of changes on the mountain. Their website, stromboli.net, contains some of the most dramatic volcano pictures ever taken.
Q: [...]{Consults list.} The last one then is do we want to ask about the confused sky the other day? (L) Oh yeah, we were driving home from the fabric store the other day, and as we were coming along, we saw every single kind of cloud in the sky. There were roll clouds to the southwest, there were high cirrus clouds, there were buttermilk-looking clouds, mare's tails, and then there was a really peculiar circular cloud that looked like a big oval smoke ring in the sky. (Andromeda) And it was in an area where it was raining and sunny at the same time. (L) It was pouring rain, the sun was shining, it was just the most bizarre thing. And every kind of cloud that is listed in cloud lists was in the sky all at the same time. It was bizarre. Any comment on our circular cloud and the other...?
A: Smoke ring, eh?
Q: (Andromeda) That's what I said! It looks like something had happened there in that area, because besides that smoke ring cloud, there was another cloud that almost had like a hole in it. This one was one that was more like a ring, and then by it was one that had the circular thing.
A: Punched from upper atmosphere air burst.
Q: (Perceval) Is that what most of those hole-punch clouds are?
A: Yes.
Q: (Perceval) Those have been around for like decades. (Kniall) It's literally a smoke ring. (L) But coming from the other direction. (Perceval) And they come up with all sorts of fancy explanations for how they form that have nothing to do with the actual cause.
Inquorate said:Smoke ring hovering over English _www.couriermail.com.au/technology/science/weird-black-ring-appears-over-english-town-leaving-experts-baffled/story-fnjwlbuh-1226885287034