Volcano tornadoes containing toxic gas have been filmed emerging from a fissure eruption in Holouhraun, Iceland.
The tornadoes were filmed by Nicarnica Aviation in Kjeller, Norway, which released the infrared footage.
"One of our NicAIR II instrments has been out in the field monitoring the ongoing fissure eruption at Holuhraun. Along with recording images of spectacular fire fountains and a sizable SO2 and water plume, we noticed something slightly unusual around 6pm on Wednesday 3rd [September]," Nicarnica said in a statement.
Scientists said that while they do not know what caused the tornadoes, "it is most likely that the generation mechanism is similar to that of dust devils which are commonly seen alongside volcanic eruptions, but in this case contains SO2 and other hot volcanic gases and ash particles".
SO2, or sulphur dioxide, is a toxic gas with a pungent, rotten smell. When inhaled, it can result in breathing difficulties in the short term. Over longer periods of exposure, S02 can worsen respiratory disease, aggravate heart disease and lead to premature death.
Commenting on the fissure eruption, Nicarnica said: "Over the weekend a new fissure eruption began at Holuhraun, a lava field north of Bardarbunga. Once again, this is not beneath the glacier and there is no ash being produced. The new fissure is estimated to be 1.5 km long and is producing lava flows and a large, white steam plume.
"The activity is visible from satellites as shown by this MODIS image where the new eruption site is indicated by the red ellipse and the steam plume is just visible through the cloud."
Fred Prata, chief technology officer at Nicarnica, told Live Science: "We haven't seen anything like this before. I was quite surprised to see it."
He added that the volcano tornado was probably a spinning ribbon of SO2, similar to a fire tornado.
The Icelandic Met Office said that earthquake activity at Bardarbunga and Holouhraun has continued over recent days, with about 30 earthquakes measured overnight.