A stunning new video of Iceland's rumbling, smoking volcano Eyjafjallajokull shows rainbow-like shockwaves belching from the crater like snakes from a can of nuts.
Nothing to fear, though, it's merely the aftereffects of Plinian events.
While rarely captured this well on film, they're not uncommon, according to vulcanologist Jim Quick, associate vice president for research and dean of grad studies at Southern Methodist University. Quick was coordinator of the volcano hazards program with the USGS, and says he's seen shockwaves like this before himself -- in person.
"We were standing on the slopes of Anatahan in the Marianas Islands," he explains, putting a series of monitoring stations around the remote Pacific island. "There were a series of these explosions hurling giant boulders above the rim. And before you could feel the shockwave, you'd see it as a series of rainbow-like structures just like this. "
Quick explained that in a vulcanian eruption like that going on at Eyjafjallajokull -- the term describes a volcano exhibiting a series of explosive bursts -- you'll see explosions called Plinian events, after the historian Pliny who described the eruption of Vesuvius in 79 AD.
These events are essentially explosive releases of gas. "You have volcanic gases that are held by the magma as it rises toward the surface. Eventually you get to the point where the gases separate from the magma, like popping the top from a soda bottle," Quick explains.
The gases expand rapidly and separate from the magma, causing explosive bursts of tremendous magnitude equivalent to a significant dynamite explosion. As the video shows, the explosion hurls incandescent blobs of lava hundreds of feet into the air -- and cause visible shockwaves.
These shockwaves reflect off the floor and the walls of the crater, shaking the entire surrounding area. In the Marianas Islands, Quick says he could feel the shockwaves rumbling beneath his feet.
"We were half a mile from the actual crater rim, and you could feel it."
Visible shockwaves aren't uncommon, occurring with any volcano having an explosive eruption, Quick explained. On the smaller scale, Plinian events cause them and lead to ejecting blobs of lava.
But Quick notes that such rumbles can have much greater ramifications.
"On the larger scale, they cause Plinian eruptions like Mt. St Helen in 1981," he pointed out.