When it comes to volcanoes, size isn't everything. 

That's according to a new study, which has found that even relatively small eruptions have the potential to cause far more global disruption than previously thought.

Scientists discovered that the last eruption of the Newberry Volcano in Oregon in 686 AD spread ash more than 3,100 miles (5,000km) across the globe - significantly further than was previously believed to be possible for a volcano of its size.

With this volcano still classed as a 'very high threat potential' by the US Geological Survey National Volcano Early Warning System, researchers warn that the risk for travel chaos is much larger than anyone had thought.

In the study, researchers from the University of St Andrews found ash particles from the blast, known as the Newberry Pumice Eruption, in Greenland ice cores.

That means the ash from the eruption travelled all the way over the North Atlantic, where it would have choked one of the world's busiest flight routes.

Lead author Dr Helen Innes told the Daily Mail: 'While not scientifically classed as a "small eruption", eruptions the size of Newberry occur globally a few times a decade and have potential to cause significant disruption to airspace and air quality.

'Future ash-rich eruptions like Newberry are going to require a coordinated international response.'

Since Greenland's ice sheet has remained relatively stable for thousands of years, scientists can use long sections of ice like frozen time capsules from Earth's past.

In their new study, Dr Innes and her team identified tiny (around 0.02 mm) particles of dust inside a core of ice.

By matching the chemical elements in the ash with volcanic deposits from the Newberry volcano's most recent eruption, the researchers discovered that they were a perfect geochemical match.

Volcanoes eject enormous quantities of ash and dust that hang in the atmosphere for months, but no one had thought they could travel quite so far from a relatively small eruption.

Dr Innes says: 'Finding so many microscopic ash particles in Greenland shows us that the eruption and conditions were able to transport the ash across the North American continent, and possibly even further across the North Atlantic. 

On the Volcanic Explosivity Index (VEI), a scale that describes the destructive power of eruptions, the Newberry Pumice Eruption is rated as a VEI-4 event.

That means it is 10 times less powerful than the VEI-5 Mount St. Helens eruption in 1980.

However, that is still 10 times larger than the VEI-3 Eyjafjallajökull Icelandic eruption, which grounded flights around the world in 2010.

This shows that a relatively small but ash-rich volcanic eruption could have an outsized impact on the world.

Eruptions can ground flights because volcanic ash melts at the high temperatures inside plane engines, clogging them with a layer of molten lava.

Small chunks of rock and glass also act like a sandblaster when planes move through them at speed, stripping paint and damaging landing lights.

The fact that researchers found ash from this American eruption in Iceland is particularly worrying, since it suggests that the blast could block a critical flight route over the Atlantic.

Scientists struggle to predict exactly when a volcano will erupt, but this discovery should help disaster planners make better preparations.

Dr Innes says: 'The volcanoes in Iceland and the US, where Newberry is located, are extremely well monitored but there are huge numbers of volcanoes that have little to no monitoring.

'This makes it extremely difficult to predict when and where the next eruption like this might take place.

Dr Innes adds: 'We need to do more to stress test our supply chain and transport networks for these sudden volcanic shocks.'

Previous studies had managed to narrow down the date of the Newberry Pumice Eruption to a 140-year window sometime around the 7th century.

However, thanks to extremely accurate dating models for Greenland ice cores, researchers have pinpointed the date to within two years of 686 AD.

Co-author Dr William Hutchinson, of the University of St Andrews, says: 'Iceland usually grabs the headlines as our restless volcanic neighbour.

'But this study is an important reminder that there are huge numbers of volcanoes across North America, Russia and Japan that can spread vast quantities of ash across the Northern hemisphere.'