Update: As of noon on Tuesday, Reyjkavik airport has reopened following the eruption of Iceland's Grimsvötn volcano -- but the ash cloud is spreading, with implications for Australia-Europe flights across the board.
As of Monday morning in Australia, Iceland's main international airport at Keflavik, just outside Reykjavik, is completely shut down due to the volcanic ash from the Grimsvötn volcano eruption, with all flights showing as cancelled.
Travellers connecting through Reyjkavik between the United States, Canada and Europe should contact their airline for further information.
An international Volcanic Ash Advisory Centre warning has been issued from the regional control centre in London, which shows the expected path of the cloud by 1200 GMT on 23 May:
The trajectory of the ash may affect flights from the west coast of the USA and Canada into the UK, France, Germany and northern Europe, which would normally fly through the path of the ash. Here's the shortest flight line from Los Angeles, San Francisco and Vancouver to three European airports:
Similarly, Australians connecting through East Asian hubs in Korea, China and Japan to European destinations should double-check with their airline, ensure their flights are on schedule and prepare for delays.
However, flights from southeast Asian hubs like Hong Kong, Singapore and Bangkok are unlikely to be affected, since they take a more southerly route to Europe, over central Asia.
Flights from the US east coast to Europe are likewise expected to be unaffected.
Of course, it's entirely possible that delays to one part of the international airline network will result in knock-on effects to the flights in completely different regions.
Iceland's most active volcano, Grimsvötn, has erupted, throwing plumes of ash into European airspace and resulting in a flight ban.
The flight ban extends 120 nautical miles (222 km) from the volcano. The ash cloud is currently considered unlikely to spread wider and affect European airspace like last year's eruption of the Eyjafjallajökull volcano, which caused widespread disruption.
Iceland's main international airport at Keflavik (KEF), just outside the capital Reyjkavik, is not expecting disruption to flights according to national carrier Icelandair.
A: Grimsvötn volcano. B: Rejykavik's Keflavik international airport
That'll be a particular relief to travellers connecting on Icelandair from Europe to the US. The airline is a favourite choice for business travellers on a budget, with well-priced fares in business, "middle seat blocked" premium economy and regular economy classes.
Last year's eruptions
It's roughly the same time of year as last year's eruptions of the Eyjafjallajökull volcano, some 150 km to the southwest of currently erupting Grimsvötn.
The air traffic shutdown over most of northern Europe from 15-23 April wreaked havoc on travellers, airlines and airports.
This year's eruption is different because high-level winds (including the north Atlantic jet stream) are in different locations. During the Eyjafjallajökull eruptions last year, the jet stream was in precisely the spot where it could suck in ash from the volcano and spread it across Europe at the same altitude used by airliners.
The current Grimsvötn eruption hasn't (yet) coincided with a jet stream.