How Etna’s Vent Shapes a Ring
A volcanic gas pulse can produce a ring when it bursts from a vent in a brief, concentrated push. As the gas rushes past the vent’s rim, friction and the difference in speed between the center and edges make it curl back on itself. The rolling loop is a vortex ring: a doughnut-shaped swirl whose gas circulates around the ring as the whole shape travels outward.
The vent’s shape and the timing of the pulse matter. A fairly round opening and a short, even burst help the flow curl into a coherent loop. A longer or uneven release is more likely to break up into less orderly turbulence instead. At Etna, such rings are a visible consequence of gas escaping through a suitably shaped opening—not a separate kind of eruption.
Why the Ring Looks White
The moving gas is largely invisible. Its moisture cools as it expands into the surrounding air, allowing water vapor to condense into tiny liquid droplets. Those droplets scatter light, tracing the circulating flow in white. The visible ring can therefore resemble smoke even though its whiteness comes from condensed water, not soot produced by burning.
As the vortex moves away from the vent, it mixes with surrounding air and loses its organized shape. The droplets evaporate or disperse, and the sharply outlined ring fades. For a moment, though, the swirl acts like a natural tracer: it makes the otherwise invisible motion of volcanic gas visible in the air above the crater.
