It’s been four years since the Eyjafjallajokull volcano in Iceland erupted, sending a massive cloud of ash into the skies and effectively bringing air travel to a halt in the normally busy North Atlantic. Now the airlines in the busiest area for international travel (and the good people of Iceland) are concerned about another Icelandic volcano that is showing signs it might erupt.

Regional air-traffic manager Eurocontrol has been looking at seismic data from the Bardarbunga volcano in Iceland and tell Bloomberg that the “seismic swarm” of earthquakes recorded around the caldera’s rim this week is the largest seen since the volcano last went “boom” in 1996. Earlier this week, officials in Iceland raised the eruption risk to “orange,” the second-highest level, and began evacuating the to the north of Bardarbunga yesterday.

The volcano’s proximity to Vatnajokull, Europe’s largest glacier, could result in a “a more explosive eruption,” explains a volcanologist, as the searing heat mixes with the melting ice.

“If the volcano erupts — which we don’t know — how explosive or non-explosive the eruption is depends entirely on where the magma reaches the surface,” she tells Bloomberg.

A seismologist cautions that “It’s still impossible to say whether or not the volcano will erupt, due to the simple fact that we can’t predict what the developments in the next hours or days will be.”

The 2010 eruption resulted in the cancellation of more than 100,000 flights and $1.7 billion in lost revenue for the airlines, that could not risk trying to navigate through or around the clouds of ash that don’t just present a visual hazard, but which can do damage to jet engines.

For the airlines there isn’t much to do other than continue flying as scheduled and hope Bardarbunga doesn’t lose its cool.

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