REYKJAVIK — Airlines are on alert as one of Iceland’s biggest volcanoes rumbles to life, threatening ash clouds that could force flight cancellations across the North Atlantic, the busiest international travel market.

Air France, Deutsche Lufthansa, EasyJet and Delta Air Lines are among carriers watching the Bardarbunga volcano. Iceland’s Civil Protection Agency has recorded about 800 earthquakes in the area since early Monday and raised the risk of an eruption to “orange,” the second-highest level.

The seismic activity raised concern that airlines may face a repeat of the 2010 disruptions when a cloud belched from the Eyjafjallajokull volcano forced carriers to erase more than 100,000 flights and caused about $1.7 billion in lost revenue. Ash represents a menace to jetliners because the glass-like particles can stop turbines by melting and congealing.

Airline traffic in Northern Europe would be disrupted “if the winds, as we’re seeing them today, continue” in a Bardarbunga eruption, said Melissa Anne Pfeffer, atmospheric volcanologist at the Icelandic Met Office.

Eurocontrol, the region’s air traffic manager, said there is currently no impact on aviation from Bardarbunga. The volcano lies beneath Vatnajokull, Europe’s largest glacier, and last erupted in 1996.

The severity of an eruption would depend on where the magma reaches the surface, Pfeffer said.