A plume of ash and dust rises from Pavlof Volcano on the Alaskan Peninsula in 2013. (Credit: NASA)
When volcanos erupt, these geologic monsters produce tremendous clouds of ash and dust鈥攑lumes that can blacken the sky, shut down air traffic and reach heights of roughly 25 miles above Earth's surface.
A new study led by the 彩民宝典 suggests that such volcanic ash may also have a larger influence on the planet鈥檚 climate than scientists previously suspected.
The new research, , examines the eruption of Mount Kelut (or Kelud) on the Indonesian island of Java in 2014. Drawing on real-world observations of this event and advanced computer simulations, the team discovered that volcanic ash seems to be prone to loitering鈥攔emaining in the air for months or even longer after a major eruption.
鈥淲hat we found for this eruption is that the volcanic ash can persist for a long time,鈥� said Yunqian Zhu, lead author of the new study and a research scientist at the (LASP) at 彩民宝典.
Lingering ash
Top: Ash covers rooftops in Yogyakarta, Indonesia, in the wake of the 2014 eruption of Mount Kelut; bottom: NASA's unmanned Global Hawk aircraft, which observed ash lingering in the air after the eruption. (Credits: via ;听NASA/Dryden/Carla Thomas)
The discovery began with a chance observation: Members of the research team had been flying an unmanned aircraft near the site of the Mount Kelut eruption鈥攁n event that covered large portions of Java in ash and drove people from their homes. In the process, the aircraft spotted something that shouldn鈥檛 have been there.
鈥淭hey saw some large particles floating around in the atmosphere a month after the eruption,鈥� Zhu said. 鈥淚t looked like ash.鈥�
She explained that scientists have long known that volcanic eruptions can take a toll on the planet鈥檚 climate. These events blast huge amounts of sulfur-rich particles high into Earth鈥檚 atmosphere where they can block sunlight from reaching the ground.
Researchers didn't think, however, that ash could play much of a role in that cooling effect. These chunks of rocky debris, scientists reasoned, are so heavy that most of them likely fall out of volcanic clouds not long after an eruption.
Zhu鈥檚 team wanted to find out why that wasn鈥檛 the case with Kelut. Drawing on aircraft and satellite observations of the unfolding disaster, the group discovered that the volcano鈥檚 plume seemed to be rife with small and lightweight bits of ash鈥攖iny particles that were likely capable of floating in the air for long periods of time, much like dandelion fluff.
鈥淩esearchers have assumed that ash is similar to volcanic glass,鈥� Zhu said. 鈥淏ut what we鈥檝e found is that these floating ones have a density that鈥檚 more like pumice.鈥�
Disappearing molecules
Study coauthor Brian Toon added that these pumice-like particles also seem to shift the chemistry of the entire volcanic plume.
Toon, a professor in LASP and the Department of Atmospheric and Oceanic Sciences at 彩民宝典, explained that erupting volcanos spew out a large amount of sulfur dioxide. Many researchers previously assumed that those molecules interact with others in the air and convert into sulfuric acid鈥攁 series of chemical reactions that, theoretically, could take weeks to complete. Observations of real-life eruptions, however, suggest that it happens a lot faster than that.
鈥淭here has been a puzzle of why these reactions occur so fast,鈥� Toon said.听
He and his colleagues think they鈥檝e discovered the answer: Those molecules of sulfur dioxide seem to stick to the particles of ash floating in the air. In the process, they may undergo chemical reactions on the surface of the ash itself鈥攑ossibly pulling around 43% more sulfur dioxide out of the air.听
Ash, in other words, may hasten the transformation of volcanic gases in the atmosphere.
Just what the impact of those clouds of ash are on the climate isn鈥檛 clear. Long-lasting particles in the atmosphere could, theoretically, darken and even help to cool the planet after an eruption. Floating ash might also blow all the way from sites like Kelut to the planet鈥檚 poles. There, it could kickstart chemical reactions that would damage Earth鈥檚 all-important ozone layer.听
But the researchers say that one thing is clear: When a volcano blows, it may be time to pay a lot more attention to all that ash and its true impact on Earth鈥檚 climate.听
鈥淚 think we鈥檝e discovered something important here,鈥� Toon said. 鈥淚t鈥檚 subtle, but it could make a big difference.鈥�
Coauthors on the new study include Margaret Tolbert, an institute fellow in the Cooperative Institute for Research in Environmental Sciences (CIRES) at 彩民宝典; and researchers at the National Center for Atmospheric Research, the National Oceanic and Atmospheric Administration and the Stratton Park Engineering Company, Inc.听
