Smoke rings from volcanos

Hey,

today I learned something cool. Under some special circumstances volcanos can do smoke  rings. Apparently it's very rare and still a mystery to the volcanologists. Here's a figure from Eyjafjallajökull volcanic eruption:

And here's a figure from Etna:

Link: http://news.discovery.com/earth/iceland-volcano-smoke-ring.html
Link: http://news.bbc.co.uk/2/hi/science/nature/696953.stm

Janne

P.s. I can do the same thing with my mouth...