A recent study: Volcanic ash affects the atmosphere and may block sunlight

When volcanoes erupt, these geological monsters produce massive clouds of ash and dust - plumes that can blacken the sky and block air traffic, reaching heights of nearly 25 miles (over 32 km) above the Earth's surface.

And a new study by the University of Colorado at Boulder suggests that this volcanic ash may have a greater impact on the planet's climate than scientists previously thought.

The new study, published in Nature Communications on September 10, examines the 2014 eruption of Mount Kelut (or Kelud) volcano on the Indonesian island of Java in 2014.

Drawing on real-world observations of the event and advanced computer simulations, the team discovered that the volcanic ash appears to have loosened and remained in the air for months or even longer after a large eruption.

“What we found in this volcanic eruption is that volcanic ash can last for a long time,” says Yunkian Chu, lead author of the new study and a research scientist at the Laboratory of Atmospheric and Space Physics (LASP) at the University of Colorado.

The discovery began with a serendipitous drone near the Mount Kilot eruption site (NASA)

Suspended ash

The discovery began with a note of accident, as members of the research team were flying a drone near the site of the Mount Kilut eruption - an event that covered large parts of Java with ash and prompted people to leave their homes.

"They saw some large, ash-like particles floating in the atmosphere a month after the explosion," Chu says.

She explained that scientists have known for a long time that volcanic eruptions can negatively affect the planet's climate, as they explode with huge quantities of sulfur-rich particles in the Earth's atmosphere and can prevent sunlight from reaching the Earth.

However, the researchers did not believe that ash could play such a large role, as scientists believed that these chunks of rock debris are so heavy that most of them likely fell from volcanic clouds not long after an eruption.

Drawing on aircraft and satellite observations of the disaster, the team discovered that the volcano's plume appears to be filled with tiny, lightweight ash particles - tiny particles that are likely to float in the air for long periods of time, like dandelion fluff.

"The researchers assumed that the ash resembled obsidian ... but what we found is that this float has a density very similar to pumice," Chu said.

A pumice is a light, porous glassy volcanic rock that fills with holes caused by gas bubbles trapped as it hardens.

The volcanic ash loaf and stayed in the air for long periods after Mount Kilot erupted (Flickr)

The disappearance of the particles

Study co-author Brian Ton added that these pumice-like particles also appear to transform the chemistry of the entire volcanic column.

Ton, a professor in the Laboratory of Atmospheric and Space Physics and the Department of Atmospheric and Ocean Sciences at the same university, explained that erupting volcanoes eject a large amount of sulfur dioxide.

The researchers previously assumed that these molecules interact with other molecules in the air and turn into sulfuric acid in a series of chemical reactions that theoretically may take weeks to complete.

But factual observations indicate that it happens much faster than that.

"There was a mystery as to why these reactions happened so quickly," Ton says.

Ton and colleagues think they've figured out the answer: These sulfur dioxide particles seem to stick to the ash particles floating in the air.

In the process, it may undergo chemical reactions on the surface of the ash itself, which would potentially cause about 43% of the sulfur dioxide to be withdrawn from the air.

Volcanic ash has a density, much like the grains of pumice rock (Flickr)

In other words, the ash may accelerate the transformation of volcanic gases into the atmosphere.

So what is the impact of those ash clouds on the climate?

It's not clear: long-lived particles in the atmosphere could, in theory, darken the planet and even help cool it after its eruption.

Floating ash may also erupt along the way from sites such as Jebel Kiloot to the planet's poles.

There, it could trigger chemical reactions that would destroy Earth's all-important ozone layer.

But researchers say one thing is clear: When volcanoes erupt, it is time to pay more attention to all this ash and its true impact on Earth's climate.