Iceland is monitoring a fissure eruption north of the Bardarbunga volcano as authorities downgraded the threat of a full-blown ash cloud.

The Icelandic Met Office lowered their aviation warning level to “orange,” after earlier raising it to the highest level following the eruption, according to an e-mailed statement. “A significant emission of ash into the atmosphere is not likely,” the agency said.

Airlines are on alert for a potential repeat of a disruption in 2010, when a volcano under the Eyjafjallajokull ice cap spewed a column of ash 9 kilometers (5.6 miles) into the air. The eruption shut airspace across Europe for six days, forcing carriers to cancel more than 100,000 flights. Ash is a danger because the glass-like particles can damage jet engines.

“Currently we’re just monitoring the eruption, which is very weak,” Rikke Pedersen, a geophysicist at the Nordic Volcanological Center, said by telephone. “The fissure could probably extend southwards or northwards and open up beneath the ice. But we’ll have to see — only time will tell.”

Volcanologists have said that water and steam from ice helped make the 2010 event so explosive, ejecting ash to cruising levels used by trans-Atlantic flights. Airlines including Deutsche Lufthansa AG, British Airways and discount specialist EasyJet Plc said they’re continuing to operate timetables as normal while monitoring the situation. Iceland’s airports are all still open, according to controller Isavia.

‘Really Small’

The eruption started from a fissure 300 meters (984 feet) long in the northern part of the Holuhraun lava flow, between the Dyngjujokull glacier and the Askja caldera, according to the Civil Protection Agency.

Bardarbunga, one of Iceland’s largest volcanoes, began rumbling two weeks ago. The volcano lies under Vatnajokull, Europe’s biggest ice cap, and has been rocked by earthquakes that led to evacuations and road closures.

“The alert levels are similar to what they were before this eruption started,” Pedersen said. “The volumes of magma that are coming up to the surface are really, really small in comparison to what we’ve seen being intruded in the past 10 days into the crust.”

The magma beneath Vatnajokull has migrated north in a dike that extends beyond the borders of the glacier, so that an eruption “would most likely produce an effusive lava eruption with limited explosive, ash-producing activity,” the Met Office said earlier.

Close Observation

“We are keeping the situation in Iceland under close observation,” British Airways, the U.K. unit of International Consolidated Airlines Group SA, Europe’s No. 3 carrier, said today. “At present all of our flights are operating normally.”

Lufthansa. the European No. 2, is monitoring the eruption and the advice of aviation authorities and sees no need to change its schedule right now, spokesman Thomas Jachnow said.

The carrier’s discount unit Germanwings, which has canceled 70 percent of flights, said Reykjavik is among destinations that it’s continuing to serve.

“We are monitoring the situation, liaising with our partners and the authorities,” Paul Moore, a spokesman for EasyJet, said today. Europe’s second-biggest discount carrier has been developing technology that can help detect ash in front of a plane, and that may be tested further if there’s a major eruption, the Luton, England-based company has said.

The company said it will work to detect ash by using infrared cameras on European weather satellites, or through the potential deployment of the AVOID detection technology.