What's the link between a peaceful bog close to the shores of Lough Neagh and a volcano in Alaska?
Scientists at Queen's University Belfast have been studying the ash layer in Sluggan Bog near Randalstown for more than 20 years, but have only just discovered that it drifted across the Atlantic Ocean from a volcano that exploded in Alaska back when the Vikings were pillaging Ireland.
The discovery that the layer matches the chemical fingerprint of the ash spewed out by Mount Bona-Churchill volcano is the first evidence that ash clouds can travel across the ocean and has major implications for the airline industry.
Researcher Dr Sean Pyne-McDonnell from the School of Geography, Archaeology and Palaeoecology said the ash layer was used by scientists as much as 20 years ago as a "time marker" to date the pollen found in the bog.
"It's a raised bog and it collects everything that pours out of the atmosphere," he said.
But it was only when he happened to fall into a discussion about the ash layer at an international conference that the "penny dropped" and the researchers realised they were all talking about the same phenomenon.
The international team has found that the ash, found in bogs across Europe, can be traced back to an eruption from the Alaskan volcano around AD847.
In 2010 plumes spewed out by the volcano Eyjafjallajokull in Iceland caused major disruption and grounded more than 100,000 international flights, costing airlines more than £2bn.
With volcanoes like Mount Bona-Churchill scheduled to erupt on average every 100 years, another ash cloud drama could be imminent, this time with consequences for transatlantic travel.
Dr Pyne-O'Donnell said the discovery was also significant in advancing knowledge across other disciplines, particularly in the area of climate change.
"The layer was deposited very quickly after eruption, probably within a matter of days, and can be used to precisely date and compare the relative timing of any environmental or archaeological events associated with it by tephro-chronology. This makes the layer very useful for researchers wanting to link together how climate behaved in distant parts of the world at this time.
"Such information is vital for climate scientists attempting to explain how climate worked in the past compared with the present. The team also speculates that other tephra layers from similar transa tlantic eruptions may yet be uncovered in other Irish sites."
The ash is from Mount Bona-Churchill. Using chemical fingerprinting, the team has matched it to a ash layer which occurs in Ireland, Norway, Germany and Greenland, where it is called the AD860B. European researchers assumed that AD860B came from a relatively close volcano in Iceland. However, the AD860B never quite fitted with what researchers knew of volcanoes in Iceland.