Making waves
An emerging story with the unfolding situation on La Palma has been remarkable atmospheric aberrations, including ring-like ripples emanating outward from around its plume.
A time-lapse video posted by Twitter user @Cielodecanarias, which translates to “Sky of the Canaries,” captured the disk-like formations accompanying the plume.
A unique set of ingredients enabled this spectacle.
When it comes to the atmosphere, air will continue rising as long as it is less dense than its surroundings. Density is usually tightly linked with temperature; warmer fluids, like air, are less dense when heated.
The volcano produced a plume of air that ascended quickly because it was warmer, and therefore less dense, than its surroundings. Like a chimney, that plume climbed 20,000 feet into the atmosphere. Eventually, the air entrained into the gaseous plume cooled slightly, becoming acutely less buoyant. But it was still rising.
Then, suddenly, it slammed into an atmospheric lid of sorts — a cap of hot, dry air, probably originating in the Sahara, several miles above the ground. That meant the plume couldn’t rise anymore and subsequently spread out and flattened. It’s analogous to why thunderstorms are marked by crisp anvil-like tops that resemble the floppy hats that chefs wear.
The updraft of a thunderstorm is relatively continuous, but the eruption of La Palma occurred in spurts and bursts. That meant irregular jolts of upward motion. Each triggered a “gravity wave” that rippled outward from there when the plume collided with the cap.