In 2010, airline companies battled a big bad smoke monster. Well...ash monster. Okay, it was a giant cloud. Still, it caused quite a bit of trouble over European airspace.

When the Eyjafjallajökull volcano erupted, more 100,000 flights were canceled, affecting 10 million people total. Bloomberg News determined the ash cost airlines almost $2 billion. The ash from the eruption can lead to a number of issues for air travel: it can clog the engines, cause power loss on the plane, and affect air courses. 

via Icelandic Met Office.

Today, the alert for the Bardarbunga volcano was raised to orange, just one below level five, red. Red means the mountain will erupt very, very soon or is currently erupting. We are just a shade of rouge away. 

The Icelandic Met Office, which sets the alert rating, told Bloomberg, "Presently there are no signs of eruption, but it cannot be excluded that the current activity will result in an explosive subglacial eruption, leading to an outburst flood and ash emission." The Met Office website also notes "Intense earthquake swarm continues at Barðarbunga. Presently there are no signs of magma moving to the surface."