Icelandic authorities have raised the volcanic alert status for aviation to its highest level after seismic instruments indicated the possible beginning of an eruption.

The Icelandic Met Office raised the aviation alert status from orange to red on Saturday after measurements suggested that an eruption had begun under the Dyngjujökull glacier, close to the Barðarbunga (Bardarbunga) volcano in southeastern Iceland.

The volcano has been the subject of close scrutiny since Aug. 16, when scientists began monitoring a swarm of earthquakes under the surface suggesting that an eruption could be imminent. Since then, thousands of earthquakes have been recorded in the vicinity of the volcano, several recorded at more than four on the Richter scale.

Airspace near the volcano has been closed, and surveillance over-flights have been stepped up, although commercial flights from Icelandic airports are continuing.

Civil protection agencies said that the eruption is currently considered a “minor event at this point.”

“Because of a pressure from the glacier cap it is uncertain whether the eruption will stay sub-glacial or not,” officials stated. They suggest the lava may remain below the glacier. If the lava does emerge onto the surface, that will happen in the next few hours—a situation that may prompt the formation of an ash cloud that could pose an danger to air traffic.

Only then will the London-based Volcanic Ash Advisory Center will begin providing assessments on the impact to regional airspace.

Eurocontrol, the Europe-wide air traffic management service said its staff were monitoring the situation and said that European air traffic authorities are ready to respond should the volcano erupt.

The service said that operational responses developed as a result of the 2010 eruption of Eyjafjallajökull, which caused more than 100,000 flights to be disrupted over six days, mean that air navigation service providers are now better prepared.