Mount Etna in Sicily recently ejected large white rings of smoke into the sky. Some of them resembled giant jellyfish.

The rings consisting of water vapor are not threatening, but are rare to observe. It's still uncertain exactly how they form, however, a circular volcanic vent with a similar height on all sides is at least one of the requirements.

The rings are thought to form when gas bubbles are forced through the narrow vent in small explosions. This forces hot vapor upwards, which literally rolls down the inside wall of the crater. This is why the vapor rings rotate around their own axis.