Bright shimmering rings rose above Mount Etna on Monday, not a sign of an eruption but another phenomenon entirely.

Mount Etna, Europe's largest active volcano, sent large halos into the sky earlier this week. These rings, which consist of water vapour, are not threatening, but they are rarely observed.

It is not clear exactly how these rings, which can reach over 600 feet wide, form. We do know that they require a circular vent with a similar height on all sides.

It is likely that the rings form when gas bubbles are impulsively forced through the narrow vent. In the process, they come under extreme pressure, explode and push the hot steam upwards.

At the same time, steam rolls up at the edge of the vent. When the rolled-up steam ring meets the cold atmosphere, the steam condenses and becomes visible, similarly to condensation trails.

Spotting this event is quite rare, but is not uncommon. Visitors to the site witnessed similar rings in May 2022.

Most of the time, the rings are twisted by the wind and destroyed again a short time after forming.

Etna is considered one of the most active volcanoes in the world, regularly releasing lava and ash onto the island of Sicily it calls home.

The volcano is so active that in 2021 so much volcanic material was expelled that the volcano actually grew by around 100 ft.