The sky was colored by ash from the eruption of Eyjafjallajökull volcano in Iceland in April. Apr. 15, 2010, Northeastern outskirts of Athens, Greece. Image © Anthony Ayiomamitis. Used with permission
The plume of ash from Iceland's Eyjafjallajökull volcano, which is now inching across Europe's skies, is creating vivid red sunsets while thwarting airline travel plans. The phenomenon could last for days, and depending on how long the volcano continues to erupt, it could spread volcanic clouds all around the Northern Hemisphere, a scientist says.
The volcanic sunsets might even be glimpsed from the United States if the volcano keeps erupting, but chances for that are slim, experts say.
"Once it stops erupting it will take a few days to settle out. As long as there's ash in the atmosphere or any pollutant for that matter, you'll see these alterations in the color we see in the sky," said Jay Miller, a volcanologist at Texas A&M University.
Onlookers are already attesting to the multihued effects.
Yesterday, one sky gazer along the outskirts of Athens, Greece, captured the sunset enshrouded by billows of smoke, noting "what caught my attention is the fact that two of my German shepherds had their nose pointed at a 45-degree angle and sniffing the air," Anthony Ayiomamitis told Spaceweather.com.
Another onlooker, Gareth Pinckard, shot a scene from Snaefell Mountain in Ireland saying, "Unbelievably vivid colors, the colors did not look real!!"
Here's what's behind the sunsets:
Once ejected into the atmosphere, the sulfur dioxide spewed from volcanoes can react to form sulfate aerosols, which are tiny particles suspended in the air. Both ash and aerosols can scatter the sun's rays, giving a sunset its apparent color. Since the plume hasn't made its way into a part of the upper atmosphere called the stratosphere, we're likely to see more reds and oranges in sunsets, rather than purple colors, according to Brian Toon, chair of the University of Colorado, Boulder's atmospheric and oceanic sciences department.
Particles in the air normally scatter incoming sunlight — this is why the sky is blue. Sunsets (and sunrises) appear reddish because the sun's rays have more of the atmosphere to travel through when they are low on the horizon, versus when they are high in the sky during the day. When the rays have more atmosphere to travel through, only the longer waves at the red end of the spectrum can make it. Sulfate aerosols in particular can intensify this effect by adding more obstacles for the light to get through.
And under certain circumstances, purple sunsets will result.
"If there's a volcanic cloud in the stratosphere, the [sun's] light will bounce back to your eye and you'll see it," Toon said in a telephone interview today. "It looks purplish, because the ozone absorbs the red light and air molecules scatter away the blue and you are left with the purple color."
Colorful sunsets for all?
How long the volcanic plume persists and where it travels depends on Mother Nature – whether the volcanic eruption continues, how the prevailing winds take shape, rain and other weather factors.
"That ash is likely to hang around for a few days after the eruption is completed," Miller told LiveScience. "We don't have any way of knowing how long this eruption will continue. Historically in Iceland over the past 1,000 to 1,500 years most of the eruptions only last a few days. Some last for a few weeks. A very few have lasted for significantly longer than that."
He added, "As long as the eruption continues and there's plenty of ice in the middle of this glacier for this magma to react with," we'll see the ash plume.
The ash, which consists of jagged bits of glassy materials, is created when the sizzling hot magma pours out of the volcano and hits the cold glacial ice.
"Imagine if you took a glass and put it into a furnace and got it red hot and dropped it into a bucket of cold water," Miller said. "It would just shatter into a billion pieces." That's essentially what's happening when the lava hits the surrounding ice to create the huge ash plume.
The prevailing winds will push the cloud in different directions and so as you get farther away from the initial plume, the ash particles will disperse more.
Even so, "I think we'll see evidence of this certainly throughout Europe for days to come after this episode, after it stops," Miller said.
But rain could wash away the chance of colorful sunsets in the United States.
"It's unlikely any of this volcanic ash will get as far as the United States," Toon said. "But it is possible. It's just rare. It's likely the stuff will get washed out before it ever gets here."
Essentially, it would likely disperse or fall out of the atmosphere before the prevailing winds (which move west to east at the latitudes of Iceland) could move it all the way around the globe.